I'm new to C++ coding and just started solving competitive programming problems. I want to solve the following task: https://onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1620.
I want to find a substring of a string. The problem is that the code below is slow and I fail the submission by getting the "time limit exceeded" "error". What can I do to speed up the code?
#include <iostream>
#include <sstream>
#include <stdio.h>
#include <string.h>
using namespace std;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
stringstream ss;
string m;
char prob[100000];
char substring[1000];
int howManyCases = 0;
int numberOfTests = 0;
cin >> numberOfTests;
cin.ignore();
while(numberOfTests--)
{
cin >> prob >> howManyCases;
while(howManyCases--)
{
cin >> substring;
if (strstr(prob,substring)) {
ss << 'y' << "\n";
}
else
{
ss << 'n' << "\n";
}
}
}
m = ss.str();
cout << m;
return 0;
}
i would make you of <algorithm> header:
std::string parent_string = "some string lala";
std::string sub_string = "lala";
auto found = parent_string.find(sub_string);
it will return iterator to where substring is. Then I wou;d use this clause:
if (found != std::string::npos) std::cout << "y\n";
else std::cout << "n\n";
If there is no limitation to the use of standard libraries, It's always a better choice to use it instead of creating your own algorithms (that may not handle some special cases you won't think of ).
Also, swap those huge ugly c-style arrays to std::string.
Related
hi guys so my question is how to convert a char array to a string. here is my code:
#include<iostream>
using namespace std;
int main()
{
while (true) {
char lol[128];
cout << "you say >> ";
cin.getline(lol,256);
cout << lol << endl;;
}
return 0;
}
so I want to convert lol to a string variable like "stringedChar" (if thats even english lol)
so I can do stuff like:
string badwords[2] = {"frick","stupid"};
for (int counter = 0; counter < 2;counter++) {
if(strigedChar == badwords[counter]) {
bool isKicked = true;
cout << "Inappropriate message!\n";
}
}
Sorry im just a c++ begginer lol
Do something like this :
as char lol[128];
into string like: std::string str(lol);
Line : cin.getline(lol,256); <--> should be changed to cin.getline(lol,128)
Just invoke std::getline() on a std::string object instead of messing about with a char array, and use std::set<std::string> for badwords as testing set membership is trivial:
#include <iostream>
#include <set>
#include <string>
static std::set<std::string> badwords{
"frick",
"stupid"
};
int main() {
std::string line;
while (std::getline(std::cin, line)) {
if (badwords.count(line) != 0) {
std::cout << "Inappropriate message!\n";
}
}
return 0;
}
Note that this tests whether the entire line is equal to any element of the set, not that the line contains any element of the set, but your code appears to be attempting to do the former anyway.
First off, you have a mistake in your code. You are allocating an array of 128 chars, but you are telling cin.getline() that you allocated 256 chars. So you have a buffer overflow waiting to happen.
That said, std::string has constructors that accept char[] data as input, eg:
#include <iostream>
using namespace std;
int main()
{
while (true) {
char lol[128];
cout << "you say >> ";
cin.getline(lol, 128);
string s(lol, cin.gcount());
cout << s << endl;;
}
return 0;
}
However, you really should use std::getline() instead, which populates a std::string instead of a char[]:
#include <iostream>
#include <string>
using namespace std;
int main()
{
while (true) {
string lol;
cout << "you say >> ";
getline(cin, lol);
cout << lol << endl;;
}
return 0;
}
The final element in the vector is the char to search for.
Here’s my code:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
vector<string> words;
string in;
while(cin>>in)
{
words.push_back(in);
}
int size = words.size()
string check = words.at(size-1);
}
I tried your code and the loop was infinite. Try asking a set number of words then use the find method for each string. Here's an example.
#include <iostream>
#include <vector>
#include <string>
using namespace std;
int main()
{
vector<string> words;
string in;
cout << "Enter 5 words: \n";
for (int i{0}; i < 5; ++i)
{
cout << "Word: ";
cin >> in;
words.push_back(in);
}
cout << "What character do you want to search for? ";
char c;
cin >> c;
for (auto word : words)
{
if (word.find(c) != string::npos)
{
cout << "Character \"" << c << "\" found in " << word << endl;
}
}
return 0;
}
Edit: I noticed that you tried to use int to store the size for the string. Use size_t instead. I also think you meant to use the length method of the string, which also returns size_t.
I am trying to this function to return without numbers, spaces, or other characters and I am supposed to use the .erase function. I understand that my loop keeps going out of range, but I have no clue how to fix it and I've been stuck on this for a while. If the user types "dogs are a lot of fun" and I need the function to return and output "dogsarealotoffun" Thanks for the help.
#include <iostream>
#include <cctype>
#include <cstring>
using namespace std;
//function to output string without spaces, numbers, or punctuations
string alphabetOnly (string input){
int size;
int i= 0;
size = (int)input.size();
while (input[i] < size){
if (isalpha(input[i])){
i++;
}
else
input.erase(input[i]);
}
return input;
}
int main() {
string input;
cout << "Enter a string to test: ";
getline(cin, input);
cout << "alphabetOnly: " << alphabetOnly(input) << endl;
}
EDITED: I was too hasty in my previous answer (as I am learning I need to speak from tested code rather than off the top of my head) and needed to debug. The problem is in the else case you need to erase the char, NOT increment i because the length of the string just changed, and also since the length of the string changed you need to reset size to be the new length. Sorry for the hasty answer earlier, I was speaking without actually using the compiled code.
#include <iostream>
#include <cctype>
#include <string>
//function to output string without spaces, numbers, or punctuations
std::string alphabetOnly (std::string input){
int size;
int i= 0;
size = (int)input.size();
while (i < size){
if (isalpha(input[i])){
i++;
}
else{
input.erase(i,1);
//do not increment i here since the index changed becauase of erase
size = (int)input.size();
}
}
return input;
}
int main() {
std::string input;
std::cout << "Enter a string to test: ";
std::getline(std::cin, input);
std::cout << input;
std::cout << "alphabetOnly: " << alphabetOnly(input) << std::endl;
return 0;
}
something like this:
#include <iostream>
#include <string>
#include <algorithm>
//function to output string without spaces, numbers, or punctuations
std::string alphabetOnly (std::string input)
{
auto not_alpha = [](char c) { return !std::isalpha(c); };
input.erase(std::remove_if(begin(input),
end(input),
not_alpha),
std::end(input));
return input;
}
int main() {
std::string input;
std::cout << "Enter a string to test: ";
getline(std::cin, input);
std::cout << "alphabetOnly: " << alphabetOnly(input) << std::endl;
}
http://coliru.stacked-crooked.com/a/340465d41ecd8c8e
There's quite a few things wrong with your code, but to start with here's your main error corrected.
#include <iostream>
#include <cctype>
#include <cstring>
using namespace std;
//function to output string without spaces, numbers, or punctuations
string alphabetOnly (string input){
int size;
int i= 0;
size = (int)input.size();
while (i < size){
if(isalpha(input[i]))
{
i++;
}
else
input.erase(input.begin( ) + i );
}
return input;
}
int main() {
string input;
cout << "Enter a string to test: ";
getline(cin, input);
cout << "alphabetOnly: " << alphabetOnly(input) << endl;
}
But this is awfully inefficient because you swhift all the remaining unchecked characters each time you delete.
You should use something like
input.erase( remove_if( input.begin(), input.end(), not( isalpha ) ), input.end( ));
This is known as the remove-erase idiom, whihc you can lookup anywhere.
I'm working on a problem where I need to have user input a message then replace the work "see" with "c". I wanted to read in the array message[200] and then break it down into individule words. I tried a for loop but when I concatinate it just adds the privous words. I am only to use array of characters, no strings.
const int MAX_SIZE = 200;
int main(){
char message[MAX_SIZE]; //message array the user will enter
int length; // count of message lenght
int counter, i, j; //counters for loops
char updateMessage[MAX_SIZE]; //message after txt update
//prompt user to
cout << "Please type a sentence" << endl;
cin.get(message, MAX_SIZE, '\n');
cin.ignore(100, '\n');
length = strlen(message);
//Lower all characters
for( i = 0; i < length; ++i)
{
message[i] = tolower(message[i]);
//echo back sentence
cout << "You typed: " << message << endl;
cout << "Your message length is " << length << endl;
for( counter = 0; counter <= length; ++counter)
{
updateMessage[counter] = message[counter];
if(isspace(message[counter]) || message[counter] == '\0')
{
cout << "Space Found" << endl;
cout << updateMessage << endl;
cout << updateMessage << " ** " << endl;
}
}
return 0;
}
After each space is found I would like to output one work each only.
You should really try to learn some modern C++ and standard library features, so you don't end up writing C code in C++. As an example, this is how a C++14 program makes use of standard algorithms from the library to do the job in 10-15 lines of code:
#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
int main()
{
using namespace std::string_literals;
std::istringstream input("Hello I see you, now you see me");
std::string str;
// get the input from the stream (use std::cin if you read from console)
std::getline(input, str);
// tokenize
std::vector<std::string> words;
std::istringstream ss(str);
for(std::string word ; ss >> word; words.push_back(word));
// replace
std::replace(words.begin(), words.end(), "see"s, "c"s);
// flatten back to a string from the tokens
str.clear();
for(auto& elem: words)
{
str += elem + ' ';
}
// display the final string
std::cout << str;
}
Live on Coliru
This is not the most efficient way of doing it, as you can perform replacement in place, but the code is clear and if you don't need to save every bit of CPU cycles it performs decently.
Below is a solution that avoids the std::vector and performs the replacement in place:
#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
int main()
{
std::istringstream input("Hello I see you, now you see me");
std::string str;
// get the input from the stream (use std::cin if you read from console)
std::getline(input, str);
// tokenize and replace in place
std::istringstream ss(str);
std::string word;
str.clear();
while (ss >> word)
{
if (word == "see")
str += std::string("c") + ' ';
else
str += word + ' ';
}
// display the final string
std::cout << str;
}
Live on Coliru
I'm trying to make a program that flips the words you input. The problem comes when I try to write the word and it asks twice for the input:
cin >> Arr >> myStr;
It is logical that it ask twice but everytime I try to use getline the compiler gives out an error (and even if it worked I have to give the input twice) and I need it to include spaces in the character array.
Here is my full code:
#include <iostream>
#include <string>
using namespace std;
string myStr;
string newVal;
int i;
int main()
{
char Arr[i];
cout << "Enter: ";
cin >> Arr >> myStr;
for (i = myStr.length(); i >= 0; i--)
{
cout << Arr[i];
}
cout << endl;
return 0;
}
The loop works.
The first problem can be corrected by achieving the proper use of getline.
The second one, I have got no idea (use a single input to assign two variables).
Thanks in advance, and I apologise if this is too much of a ridiculous question.
Maybe you can try to have a look to this solution that it's more C++ style than yours:
#include <iostream>
#include <string>
int main() {
std::string myStr;
std::cout << "Please give me a string: ";
if(std::getline(std::cin, myStr)) {
for(std::string::reverse_iterator it = myStr.rbegin();
it != myStr.rend();
++it) {
std::cout << *it;
}
std::cout << std::endl;
}
}
I suggest to you to use always std::string in C++ because has all the methods and function that you could need. So don't waste your time with char array like you do in C.
Here it is, as I said. I was digging around and came up with this:
#include <iostream>
#include <string>
using namespace std;
string myStr;
int i;
int main()
{
cout << "Enter: ";
getline (cin, myStr);
i = myStr.size();
cout << i << endl;
char Arr[i];
for (int a = 0; a <= i; a++)
{
Arr[a] = myStr[a];
}
for (i; i >= 0; i--)
{
cout << Arr[i];
}
return 0;
}
I did not know string contents could also have array-like behaviour. Test it out! Works like a charm (as far as tested).
The way I formatted the code it takes no more than 27 lines of code.
Thanks everyone involved, you helped me a lot.
P.S: Couldn't answer before, I can't do it soon enough with my reputation.