Given a string s, check if it is possible to make it a palindrome by deleting AT MOST one character (meaning zero deletions is acceptable). String s will contain <50,000 lowercase alphabetical characters.
The code I wrote below passed 458/460 test cases, and it got stuck on one in particular with no obvious reason, returning false instead of true. The logic of the algorithm is simple, and I've tried moving conditionals around but nothing seems to change.
class Solution {
public:
bool ispalindrome; //holds result
bool validPalindrome(string s) {
bool candelete = true; //allows one delete
ispalindrome = true; //initial condition
int lcursor = 0;
int rcursor = s.length() - 1;
while(lcursor < rcursor && ispalindrome){
//if cursor points at different letters
if(s[lcursor] != s[rcursor]){
// if delete is still allowed and delete works
if(s[lcursor + 1] == s[rcursor] && candelete){
lcursor++;
candelete = false;
} else if (s[lcursor] == s[rcursor - 1] && candelete){
rcursor--;
candelete = false;
} else {
ispalindrome = false;
}
}
lcursor++;
rcursor--;
}
return ispalindrome;
}
};
The test case that trips this solution is as follows:
aguokepatgbnvfqmgmlcupuufxoohdfpgjdmysgvhmvffcnqxjjxqncffvmhvgsymdjgpfdhooxfuupuculmgmqfvnbgtapekouga
Code testing with this testcase:
#include <iostream>
using std::string;
// class Solution { ... etc., from above
int main() {
string s = "aguokepatgbnvfqmgmlcupuufxoohdfpgjdmysgvhmvffcnqxjjxqncffvmhvgsymdjgpfdhooxfuupuculmgmqfvnbgtapekouga";
std::cout << Solution().validPalindrome(s) << std::endl;
};
If there is a case where the cursor points at different letters, and a character can be deleted from either the left or right cursors, your algorithm will only check with a delete from the left. If a palindrome is formed by deleting from the right, instead, your code will miss it.
So if you delete from the left, you need to also check if a delete from the right is possible and (potentially) check that if there is no palindrome when deleting from the left.
Related
I am currently doing games on my free time and am currently working on a hangman game. However, I have stumbled upon a problem and I think I could solve it if there was a way to run a statement if a condition inside a loop is met at least once, and if the condition isn't met even once, it'll do another thing. Is it possible to do? Does anyone have any ideas?
I appreaciate any suggestions.
I tried doing something like this:
for (){
if (string [i] == letter that the player inputed){
// replace underscores with the letter guessed
// and also turn a bool statement true
}
else {
// turn the bool statement false
}
}
if (!bool variable){
// print that the letter guessed was not in the answer
// and substract one from the number of guesses available
}
However I noticed that it doesn't work because the loop will run and if the last letter that it checks is not in the answer, the bool will turn false, thus printing that the letter was not in the answer and substracting one from the score. (It's also my first time posting here, and I don't know if that's how I'm supposed to write a code, so I apologize beforehand if I'm not doing it correctly)
`
You should approach this problem from the different angle:
for( ... ) {
if( your condition is met ) {
do_whatever_you_have_to();
break; // <<--- exit the loop, so it's done only once
}
}
You don't have to put flag guessed off if the comparation fails
string s;
bool guessed = false;
char inputted_letter; // comes from somewhere
for (size_t i = 0; i < s.size(); ++i) {
if (s[i] == inputted_letter) {
// replace underscores with the letter guessed
guessed = true;
}
}
if (!guessed) {
// print that the letter guessed was not in the answer
// and substract one from the number of guesses available
}
You don't have to set false in the loop:
bool has_found = false;
for (auto& c : word_to_guess)
{
if (input_letter == c) {
// replace _ by current letter...
has_found = true;
}
}
if (!has_found){
// print that the letter guessed was not in the answer
// and substract one from the number of guesses available
}
But I suggest that your loop does only one thing at a time:
bool contains(const std::string& word_to_guess, char input_letter)
{
return std::any_of(word_to_guess.begin(),
word_to_guess.end(),
[&](char c){ return input_letter == c; })
/*
for (auto& c : word_to_guess)
{
if (input_letter == c) {
return true;
}
}
return false;
*/
}
if (contains(word_to_guess, input_letter)
{
// show current letter...
for (std::size_t i = 0; i != hangman_word.size(); ++i) {
if (word_to_guess[i] == input_letter) {
hangman_word[i] = word_to_guess[i];
}
}
} else {
// print that the letter guessed was not in the answer
// and substract one from the number of guesses available
}
Can you do what you are asking; possibly, however you stated you were making the game Hangman in C++ and I think you are going about this with the wrong approach, therefore, choosing or implementing the wrong algorithms. You are trying to traverse through two strings with possible different lengths from the back end which if it isn't done correctly can lead to issues, will tend to be hard to track especially if their comparisons determine loop conditions, exit or return statements.
I have implemented my version of "Hangman", now albeit the formatting isn't the prettiest, nor are the level dictionaries being generated from a large pool of random words. I express this in the comments of the code that these would generally be read in from a text file and saved into these structures. For simplicity's sake, I initialized them with random words directly in the code.
Take a look to see what I've done:
#include <string>
#include <iostream>
#include <vector>
#include <map>
#include <random>
class Game;
int main() {
using namespace util;
try {
Game game("Hangman");
game.start();
} catch (const std::exception& e) {
std::cerr << e.what() << std::endl;
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
class Game {
private:
std::string title_;
bool is_running_{ false };
std::string answer_;
std::string guessed_;
std::map<unsigned, std::vector<std::string>> dictionary_; // unsigned represents difficulty level of word
unsigned choosen_difficulty_;
std::string guessed_characters_{"\n"};
public:
Game(const std::string& title) : title_{ title }, choosen_difficulty_{ 0 } {
initialize();
start_over();
}
void start() {
is_running_ = true;
// the player has as many attempts as twice the length of hidden answer's word length.
int number_tries = answer_.size() * 2;
while (is_running_ || number_tries > 0) {
displayGuessedWord();
displayGuessedCharacters();
// ask the player to guess a character;
char guess;
// get a character and make sure it is a valid alphabet character
do {
std::cout << "Guess a character ";
std::cin >> guess;
// Note: I'm using ascii characters in this case
// but for demonstration purposes only!
if ((guess < 'a' && guess > 'z') ||
(guess < 'A' && guess > 'Z')) {
std::cout << "invalid entry ";
}
} while ( (guess < 'a' && guess > 'z') ||
(guess < 'A' && guess > 'Z') );
// test character and update guessed word and number of tries.
test_character(guess);
update_guessed_characters(guess);
number_tries--;
// failed condition
if (number_tries <= 0 && guessed_ != answer_) {
std::cout << "\nGame Over!\n";
is_running_ = try_again(number_tries);
// winning condition
} else if (number_tries > 0 && guessed_ == answer_) {
std::cout << "\nCongratulations!\n";
is_running_ = try_again(number_tries);
}
if (!is_running_) break;
}
}
private:
void displayGuessedWord() {
std::cout << '\n' << guessed_ << '\n';
}
void displayGuessedCharacters() {
std::cout << guessed_characters_ << '\n';
}
void initialize() {
// Normally this would be read in from a file upon game initialization
// but for demonstration purpose, I'll generate a few small vectors of strings
// and associate them to their difficulty level
// levels are based on 3 factors, the length of the word, the repetitive occurance
// of common characters, and the amount of less commonly used characters.
std::vector<std::string> level_1{ "ate", "cat", "dog", "coat", "coal", "does" };
std::vector<std::string> level_2{ "able", "believe", "balloon", "better", "funny", "happy" };
std::vector<std::string> level_3{ "ability", "carpenter", "dogmatic", "hilarious", "generosity", "hostility" };
// ... etc. I'll use just these here for simplicty where each vector has six entries, however,
// with random number generators, this can be done generically for any size
// or number of elements in each of the different vectors.
// create generate the map:
dictionary_[1] = level_1;
dictionary_[2] = level_2;
dictionary_[3] = level_3;
}
std::string getWordFromDictionary(unsigned difficulty, std::map<unsigned, std::vector<std::string>>& dict) {
auto level = dict[difficulty]; // extract the vector based on difficulty level
auto size = level.size(); // get the size of that vector
std::random_device dev; // create a random device
std::mt19937 rng(dev()); // create a pseudo random generator
// create a uniform int distribution type with the range from 0 to size-1
std::uniform_int_distribution<std::mt19937::result_type> dist(0, size - 1);
return level[dist(rng)]; // return a random string from this level.
}
void start_over() {
system("cls"); // Note: I'm running visual studio on Windows!
std::cout << "Welcome to " << title_ << '\n';
// We can use a random generator to pick a word from the given difficulty
// but first we need to get user input for the chosen level.
do {
std::cout << "Choose your difficulty [1-3]\n";
std::cin >> choosen_difficulty_;
if (choosen_difficulty_ < 1 || choosen_difficulty_ > 3) {
std::cout << "Invalid entry:\n";
}
} while (choosen_difficulty_ < 1 || choosen_difficulty_ > 3);
answer_ = getWordFromDictionary(choosen_difficulty_, dictionary_);
// clear and resize guessed word to be that of answer_ and add bunch of hypens.
guessed_.clear();
guessed_.resize(answer_.size(), '-');
// also reset the guessed_characters
guessed_characters_ = std::string("\n");
}
bool try_again(int& tries) {
std::cout << "Would you like to try again?\n";
char c;
std::cin >> c;
if (c == 'y' || c == 'Y') {
start_over();
// don't forget to update this so that the loop can repeat
tries = answer_.size() * 2;
return true;
}
else {
std::cout << "Thank you for playing " << title_ << '\n';
return false;
}
}
void test_character(const char c) {
// here is where you would use the standard library for taking the character
// passed into this function, updating the guessed_characters
// get all indexes
std::vector<unsigned> locations;
for (unsigned i = 0; i < answer_.size(); i++)
if (answer_[i] == c)
locations.push_back(i);
// now update the guessed word
if ( locations.size() > 0 )
for (size_t n = 0; n < locations.size(); n++)
guessed_[locations[n]] = c;
}
void update_guessed_characters(const char c) {
guessed_characters_.insert(0, &c); // just push to the front
}
};
If you noticed how I structured the game class above; I am using while and do-while loops in conjunction with for-loops and if-statements and a single boolean flag to determine the state of the game. The game state is also determined from the update to the guessed characters and guessed word. Then I compare that to the answer. Depending on certain conditions the loop will continue seeking input from the user or will exit.
I am not guaranteeing that this code is 100% bug-free for I didn't do any rigorous testing or checking corner cases or special cases but the code has run without error and I've tested all primary game state cases. It appears to be working fine.
I know that there could be many improvements and simplifications made if I had chosen to use some of the standard library functions for working with strings, but I wanted to illustrate the individual steps that are involved in the design or thinking process of making a game with states and their transitions. I could of also put the game class declaration into its own header file with its implementation in a cpp file, but I left that as a single class that is shown in main.cpp for easy copy and paste and compilation.
With this particular game, I did not use a switch and case statements, I just stuck with some while and do-while loops, a few for loops, and if statements since there are only a few game states and transitions to worry about. This implementation also demonstrates the algorithms that are involved and shows how they interconnect with each other. I hope this helps to give you a better understanding of the design process.
When making a game that has different states with a bit of complexity to it, you should start by making your state table first and list all of its transitions before you even write any code. Then you should list your starting, continuing, winning, failing and exiting states or cases. Then you need to draw up how you would transition from one state to another by their required conditions. This will help you in the long run!
Once you have the game state and its transitions laid out properly, then you can start to make your required functions for those states and begin to connect them together. After that is when you would write the internal of the functions or their implementation of what they would do.
Finally, after you have that down is where you want to do some debugging and unit and case testing and if everything appears to be okay, then it would be safe to improve your current algorithms or choosing better ones for peak or most efficient performance.
First of all sorry for too much code
Here there is a vector (teamNum) with type class, the class contain a vector (player) with type struct, it is a little complicated, but here in this function I need to check if there is a player in teamNum which contain tName equal to _tname (function parameter) contain (the player) pID equal to _pID (function parameter)
bool thereIsSimilarID(string _tname, int _pID)
{
for (int i = 0; i < teamNum.size(); i++)
{
if (teamNum[i].tName == _tname)
{
for (int j = 0; j < teamNum[i].player.size(); j++)
{
if (teamNum[i].player[j].pID == _pID)
return true;
}
}
else if (i == (teamNum.size() - 1))
{
return false;
}
}
}
And in the main
int main()
{
cout << "\n" << thereIsSimilarID("Leverpool", 1) << endl;
}
The output is 24 !!!!!
(good note that this happen just when the team (Leverpool) is the last team in the vector teamNum)
Again sorry for too much code but I need to know the bug not only fix the problem I need to learn from you
You encountered undefined behaviour.
If you take the if (teamNum[i].tName == _tname)-branch on the last element, but find no player with the correct pID, you don't return anything. Which means, that the return value is whatever random value is currently in the memory location that should hold the return value. In your case it happens to 24. But theoretically, everything could happen.
The same problem occurs when teamNum is empty.
The solution is to make sure to always return a value from a function (except if it has return type void of course):
bool thereIsSimilarID(string _tname, int _pID)
{
for (int i = 0; i < teamNum.size(); i++)
{
// In this loop return true if you find a matching element
}
// If no matching element was found we reach this point and make sure to return a value
return false;
}
You should take a look at your compiler settings and enable all the warnings. And often it's good to let it treat certain warnings as errors.
I'm trying to create a program for an assignment that will add and remove strings from a vector of strings, but first I need to create a function that will find whether or not the string already exists in the vector.
I've already tried to use a loop to search through the vector to find a specific desired string at each index. I tried adding a break; to exit if the string was found. I don't know if the function is supposed to be void or boolean.
bool FindString(int vctrSize, vector<string> restaurantVctr, string targetRestnt) {
int i;
for (i = 0; i < vctrSize; ++i) {
if (restaurantVctr.at(i) == targetRestnt) {
return true;
break;
}
else {
return false;
}
}
}
I expect the output to be true if the string was found, else it would obviously be false.
Edit: I forgot to mention that I also received the warning: "not all control paths return a value"
You should use std algorithms whenever possible:
auto result = std::find(restaurantVctr.begin(), restaurantVctr.end(), targetRestnt);
return result != restaurantVctr.end();
That is exactly what std::find is for.
While I recommend using std::find as others have recommended, if you're curious what is wrong with your code, the problem is your else:
for (i = 0; i < vctrSize; ++i) {
if (restaurantVctr.at(i) == targetRestnt) {
return true;
break;
}
else {
return false;
}
}
If the first item in your vector is not equal to targetRestnt, then your function returns--that is, it ends execution.
You only want to return false if it's not in the whole list--that is, you want the whole loop to execute:
for (i = 0; i < vctrSize; ++i) {
if (restaurantVctr.at(i) == targetRestnt) {
return true;
// Also, you don't need a break here: you can remove it completely
// For now, I just commented it out
// break;
}
}
// We didn't find it:
return false;
I am currently working a program where I am inserting words into a trie. Currently my insert function only adds in the first letter of the word and then stops. From everything I have looked up, my code looks correct, so I don't understand what the issue is.
I have tried moving the temp-> wordEnd = true to the outside of the for loop and within different locations in the function. For I believe this is the problem, due to everything else in my insert function looking correct.
Here is my insert function:
bool Trie::insert(string word)
{
TrieNode *temp = root;
temp->prefixAmount++;
for (int i = 0; i < word.length(); ++i)
{
int currentLetter = (int)word[i] - (int)'a';
if (temp->child[currentLetter] == NULL)
{
temp->child[currentLetter] = new TrieNode();
temp->child[currentLetter]->prefixAmount++;
temp = temp->child[currentLetter];
}
temp->wordEnd = true;
return true;
}
}
Also to help everyone follow my code a little bit better
Here is my TrieNode struct:
struct TrieNode
{
int prefixAmount;
struct TrieNode *child[ALPHA_SIZE];
bool wordEnd;
};
And here is my Trie constructor:
Trie::Trie()
{
root = new TrieNode();
root->wordEnd = false;
root->prefixAmount = 0;
}
The expected results are suppose to be that the whole word get inserted.
What actually happens is that only the first letter of the word gets added.
I've reformatted the code for you, and now you should hopefully see the main issue.
You are returning at the end of the block within the for loop. This will mean that it runs the first iteration of the for loop and just return without considering the rest of the letters.
An easy fix would be to put the return outside the for loop but there is another issue that you dont properly update the Trie if the current letter is already in it. Your NULL check is correct, but you should only new up the TrieNode on NULL but you also want to run all subsequent lines even if its not NULL. Fixed code will look like:
bool Trie::insert(string word)
{
TrieNode *temp = root;
temp->prefixAmount++;
for (int i = 0; i < word.length(); ++i)
{
int currentLetter = (int)word[i] - (int)'a';
if (temp->child[currentLetter] == NULL)
{
temp->child[currentLetter] = new TrieNode();
}
temp->child[currentLetter]->prefixAmount++;
temp = temp->child[currentLetter];
}
temp->wordEnd = true;
return true;
}
(Other minor issues in the code outside the scope of the question - prefer nullptr to NULL, why return a bool if its always true, if your string contains anything outside of a-z then you'll read outside the array bounds, prefer unique_ptr and make_unqiue to raw new/delete).
my knowledge is limited, writing in C++ for 2 months
In this function string code is recursively decrements chars until the base case "" is found. I want to prune some paths before the base case is found, and for some string code a path to the base case will not be found. For the prune I want to compare an attribute in the path with parameter int time. This searches a trie made of 'nodeT'
struct charT {
char letter;
nodeT *next;
};
struct nodeT {
bool isOperation;
bool isCode;
int time;
Vector<charT> alpha;
};
nodeT *root
usage:
string code = "12345";
int time = convertToEpoch(20120815); //my epoch function
containsCode(code, time)
bool containsCode(string code, int time)
{
if(root == NULL) return false;
else return containsCodeHelper(root, code, time);
}
bool containsCodeHelper(nodeT *w, string code, int time)
{
if(code == "") //base case: all char found
return w->isCode;
else {
if (w->isOperation && w->time != time) return false; //case 2: time check OK <- at a midpoint in the path
for(int i = 0; i < w->alpha.size(); i++) { //Loop through the leaf
if (w->alpha[i].letter == code[0]) //case 3: leaf exists
return containsCodeHelper(w->alpha[i].next, code.substr(1), time);
}
}
return false; //if no path
}
This function worked well before adding the time check prune, it now loops, returns false if outside time but then starts again with the candidate string code from char location 0.
Questions: 1) Is a nested return false kicking the recursion back to the next call for loop, 2) should the time prune be placed in the for loop with a logical return false or return 'path', 3) is this more fundamentally messed-up and I need to learn a C++ concept <- please explain if yes.
Also, the posted function is a simplified version of the actual function - there is a modifier to time and a 'step over' path that I left out. In past question I found that these 'addons' distract from the question.
after some reworking it now functions fine - possibly it always did; I changed to read attribute return w->isCode to return true, that seemed to be the biggest issue - I will debug the trie constructor and see if it is setting the attribute at the end of each path.
boolcontainsCodeHelper(nodeT *w, string code, int time)
{
if(code == "") //base case: all char found
return true;
else {
if ( w->isOperation && (!((w->begin-wag) <= time && time <= (w->end+wag) ) && time != 9999 ) )
return false; //case 2: time
else {
for(int i = 0; i < w->alpha.size(); i++) { //Loop through all of the children of the current node
if (w->alpha[i].letter == word[0])
return containsCodeHelper(w->alpha[i].next, word.substr(1), time, wag);
else if (word[0] == 'ΕΎ') //step over '0' all subnodes
if (containsCodeHelper(w->alpha[i].next, word.substr(1), time, wag))
return true;
}
}
}
return false; //if char is missing - meaning the exact code is not there - terminates garbage subnode paths
}
I don't see any difference between having return false; at the end and leaving it out. Also still confused as why the special case needs if( bool fn()) return true; rather than just return ( bool fn()); i found that solution through trial and error with help from another stack overflow thread