how to insert values into middle of array [duplicate] - c++

This question already has answers here:
Inserting an element into an array
(4 answers)
Closed 9 years ago.
So I have an array something like this [1,2,3,4,5,6,7,8,9] the max for this array is 15 values. What I want to do is insert an int if i call a numbers index. So say I call 5 which is index 4 from there everything shifts over and the new value is inserted [,1,2,3,4,0,5,6,7,8,9] How would I go about this?
I tried this but i can't seem to get it right it overrides the value.
int xxx;
cin >> num;
if (num >= 0 && num <= 15) {
for (int i = num; i < MAX; i++) {
values[i] = values[i+1];
cout << values[i+1] << endl;
}
viewVal(values, position);
cout << endl << endl;
}

The problem is that values[i] = values[i+1]; shifts a value one step to the left (index 4 now has the value of index 6), but you want to shift all values one step to the right. Thus, you have to reverse the assignment.
This creates the problem that once you have moved a value to the right, the previous value on the position to the right is lost. To prevent this, you can start from the back of the array.

Changing the size of plain arrays is not possible in C++. I can suggest use std::list, it supports constant time insertion.
#include <iostream>
#include <list>
#include <algorithm>
int main()
{
std::list<int> l{1, 2, 3, 4, 5, 6, 7, 8, 9};
int n;
std::cin >> n;
auto it = std::find(l.begin(), l.end(), n);
if(it != l.end())
{
l.insert(it, 0);
for(const auto& elem: l)
{
std::cout << elem << ' ';
}
std::cout << std::endl;
}
else
{
std::cout << "No such element" << std::endl;
}
return 0;
}

hope this will help, here all the elements are first shifted to the right, then the new number is inserted into array.
for(int i=(num-1);i<MAX;i++)
{
int temp=values[i];
values[i+1]=temp;
}
values[num-1]=0;

Related

my code seems perfect but showing wrong output. can someone help me what wrong am i doing here?

i have to return the max len of consecutive seq present in an array.
consider the example:-
N = 7
a[] = {2,6,1,9,4,5,3}
my code should return 6 but its giving 1. don't know how?
int findLongestConseqSubseq(int arr[], int N)
{
//Your code here
unordered_map<int,int> mp;
int ans=0;
for(int i=0;i<N;i++){
if(mp.count(arr[i])>0){
continue;
}
int len1=mp[arr[i]-1];
int len2=mp[arr[i]+1];
int ns=len1+len2+1;
ans=max(ans,ns);
mp[arr[i]-len1]=ns;
mp[arr[i]+len2]=ns;
// ans=max(ans,ns);
}
return ans;
}
There are two problems with your implementation.
The first issue is the code:
if(mp.count(arr[i])>0){
continue;
}
this code is not sufficient to ensure that repeated numbers do not make it into the rest of your loop (to see why this is, consider what happens with neither len1 or len2 are zero).
You can replace it with something like:
if(!mp.insert(pair<int,int>(arr[i], 1)).second) {
continue;
}
This will skip the rest of the loop if an entry for arr[i] exists, but also ensures that an entry will exist after the if expression is evaluated.
The second issue is with the code:
int len1=mp[arr[i]-1];
int len2=mp[arr[i]+1];
the subscript operator for maps in C++ has a side-effect of creating an entry if one does not exist. This is problematic for your algorithm because you do not want this to happen. If it did it would cause the previous piece of code to skip numbers it shouldn't. The solution is to use find but since the code for this is a little ugly (IMHO) it's probably neater to write a helper function:
inline int findOrDefault(const unordered_map<int, int>& map, int key, int defaultValue) {
auto find = map.find(key);
return (find == map.end()) ? defaultValue : find->second;
}
and use this to update your code to:
int len1=findOrDefault(mp, arr[i]-1, 0);
int len2=findOrDefault(mp, arr[i]+1, 0);
Putting this all together you end up with:
inline int findOrDefault(const unordered_map<int, int>& map, int key, int defaultValue) {
auto find = map.find(key);
return (find == map.end()) ? defaultValue : find->second;
}
int findLongestConseqSubseq(int arr[], int N)
{
unordered_map<int,int> mp;
int ans=0;
for(int i=0;i<N;i++){
if(!mp.insert(pair<int,int>(arr[i], 1)).second) {
continue;
}
int len1=findOrDefault(mp, arr[i]-1, 0);
int len2=findOrDefault(mp, arr[i]+1, 0);
int ns=len1+len2+1;
ans=max(ans,ns);
mp[arr[i]-len1]=ns;
mp[arr[i]+len2]=ns;
}
return ans;
}
Ok had a moment to look at this again and I came up with this. First we sort the array to make things easier. Then we can go through the numbers with one pass, counting each time the next consecutive number is greater by one. If the next number is not one greater after sorting, then we reset and start counting again, storing the highest streak count in max.
#include <iostream>
#include <algorithm>
#include <iterator>
using namespace std;
int main()
{
cout << "Get Longest Consecutive Streak: " << endl;
int intArray[] = { 9, 1, 2, 3, 4, 6, 8, 11, 12, 13, 14, 15 ,16 };
int arrayLength = size(intArray);
sort(intArray, intArray + arrayLength); //Sort Array passing in array twice plus amount of indexes in array
cout << "Sorted Array looks like this:" << endl; //Outputting sorted array to check
for (int i = 0; i < arrayLength; i++) {
cout << intArray[i] << " ";
}
cout << endl;
int count = 1;
int max = 1;
/*
* Loop through array, if the next number is one greater than current then add to count
* If it is not, reset the count.
* Store highest count value found passing through.
* */
for (int i = 0; i < arrayLength -1; i++) {
if (intArray[i + 1] == intArray[i] + 1) { //checking next value - is it equal to this one + 1?
count++;
}
else { //else if it is not, store the value if it is higher that what is currently there, then reset
if (max < count) {
max = count;
}
count = 1;
}
}
//Edge case: check again one more time if the current count (when finishing) is greater than any previous
if (max < count) {
max = count;
}
cout << "Longest Consecutive Streak:" << endl;
cout << max << endl;
return 0;
}

The numbers in my bubble sort array output incorrectly after being sorted [duplicate]

This question already has an answer here:
Array not playing back properly inside function - bubble sort
(1 answer)
Closed 2 years ago.
I am learning bubble sort. In my output array, the numbers in my presort array output correctly, but the second time it outputs with the sorted numbers it omits the 0 in the 10. I get an output of: Before sort: Array = {10, 2, 3, 1} After sort: Array = {1, 2, 3, 1} Any ideas?
#include <iostream>
using namespace std;
void showArray(int sortMe[], int size);
int main()
{
int sortMe[4] = {10, 2, 3, 1}; // Original Array
int numElements = 4;
int temp; // For swapping
cout << "Before sort: ";
showArray(sortMe, numElements);
for (int i=numElements-1; i>0; i--) { // For loop1
for(int j=0; j<i; j++) {
// Checks if the value on left is bigger than the right
if(sortMe[j] > sortMe[j+1]) {
// If bigger swap values
temp = sortMe[j];
sortMe[j] = sortMe[j+1];
sortMe[j+1] = temp;
}
}
}
cout << "After sort: ";
showArray(sortMe, numElements);
}
void showArray(int sortMe[], int size) {
// Outputs array in format array = {num1, num2, etc.}
int i = 0;
cout << "Array = {";
for (int i = 0; i < size - 1; i++) {
cout << sortMe[i] << ", ";
}
cout << sortMe[i] << "}" << endl;
}
Your problem is not the sorting, but printing. You define i two times.
If you rewrite your for loop inside the print like this your problem is solved for (; i < size - 1; i++).
The way you've written it the last element is always the element at index 0 because of int i = 0; outside of the loop.

ambiguous runtime error causing the program to crash immediately

#include <bits/stdc++.h>
using namespace std;
int freq[101034];
int main() {
int n;
cin >> n;
set<int> st;
for (int i = 0; i < n; i++) {
int x;
cin >> x;
freq[x]++;
st.insert(x);
}
while (!st.empty()) {
for (auto x : st) {
if (freq[x] <= 0) {
st.erase(x);
continue;
}
cout << x << ' ';
freq[x]--;
}
cout << '\n';
}
return 0;
}
The problem I have tried to solve: Given an array of integers n up to 10^5 and each element up to 10^5, the task is to print the array sorted without repetition, then delete the array elements that are printed, then repeat until the array is empty.
For instance if array [1, 1, 2, 3, 4, 4]
This should be printed
1 2 3 4
1 4
I maintained a frequency array to hold each element frequency and the code above causes runtime error. The program crashes. I've tried to remove the if statement, the program runs normally, but goes to infinite loop for sure! I really can't figure why the if causes runtime error.
The issue is in this snippet:
while (!st.empty()) {
for (auto x : st) {
if (freq[x] <= 0) {
st.erase(x);
continue;
}
cout << x << ' ';
freq[x]--;
}
cout << '\n';
}
The range-based for loop uses iterators in the back (see this for more details). When you erase x from st the loop iterator (pointing to x) becomes invalid (this means that you mustn't use it anymore), but in the snippet above, it still gets incremented at the end of the loop in the background, that result undefined behavior, hence the runtime error.
Take a look at this page to see how you should implement it properly. Applying the practice of the previous link to your code:
while (!st.empty()) {
for (auto it = cbegin(st); it != cend(st);) {
auto x = *it;
if (freq[x] <= 0) {
it = st.erase(it);
} else {
++it;
cout << x << ' ';
freq[x]--;
}
}
cout << '\n';
}

Party Invitation

The problem that I am working on right now is here, but I am of course not looking for the complete answer to this homework problem. All I am asking for is the steps in the final parts of the question. This is what I have so far:
int main()
{
cout << "Please enter the number of guests attending your party: ";
int k;
cin >> k;
cout << "Please enter the number of rounds of removal you'd like to perform: ";
int m;
cin >> m;
for (int i = 1; i <= m; i++) {
cout << "Please enter the multiple at which you'd like the removal to be at for round " << i << ": ";
int r;
cin >> r;
if (k % r == 0) {
k - r;
}
cout << k << endl;
}
system("pause");
}
This is all so confusing to me, and I truly have no idea where to turn to get answers. It seems like I'd need an array to solve this, but arrays in C++ cannot be variable, and the array length would be k, a variable input. Any help would be very appreciated.
I've read that question. you need a dynamic list like Linked list because you need to put and remove different items from different index so using arrays will be difficult.
Try to use std::vector or std::list, you can add or remove any any of list
#include <list>
std::list<int> mylist;
How can you add and remove values from list, check this link http://en.cppreference.com/w/cpp/container/list
For using your own Linklist, check this link How could i create a list in c++?
According to your question an std::vector will be the best choice because it is a combination of an array & linked list in raw terms or we can simply say it's a dynamic array.
However as you mentioned n your comment that you haven't been taught anything other than basic arrays & want a solution within whatever you have learnt, then you have to take an array. Now the problem is that arrays are static & you cannot delete elements from it. So all you can do is to keep a counter that will take care of the number of elements in it.
// array insert and delete
#include <iostream>
using namespace std;
void see_array (int a[], int f, int b)
{
for (int i=f; i<b; ++i)
cout << a[i] << ' ';
cout << '\n';
}
int get_pos (int a[], int f, int b, int num)
{
for (int i=f; i<b; ++i)
{
if (a[i] == num)
return i;
}
return -1; // if search is unsuccessful
}
int main()
{
int a[] = {1,2,3,4,5,6,7,8,9,10};
int front = 0, back = 10; // as we have 10 elements
// delete last element
--back;
see_array(a, front, back);
// delete first element
++front;
see_array(a, front, back);
// delete element from middle say 6
int pos = get_pos(a, front, back, 6);
if (pos != -1)
{
for (int i = pos; i<back; ++i) // shift elements towards left
{
a[i] = a[i+1];
}
--back; // decrease size of the array
see_array(a, front, back);
}
return 0;
}
/* Output :-
1 2 3 4 5 6 7 8 9
2 3 4 5 6 7 8 9
2 3 4 5 7 8 9
*/
I hope the above program is of some help to you !!! Good luck !!!

swap array values in c++

I want to shift left array values if my v=4 is in a[n],remove 4 from a[n] and at the end index add 0,how i can do this?
#include <iostream>
using namespace std;
const int n=5;
int main()
{
int a[n]={1,5,4,6,8}, v=4;
int b[n];
cout << "Enter a Value" << endl;
cout<<v<<endl;
for(int i=0; i<n; i++){
cout<<a[i];
}
cout<<endl;
for(int j=0; j<n; j++){
b[j]=a[j];
if(a[j]==v)
b[j]=a[++j];
cout<<b[j];
}
return 0;
}
#include <vector> // needed for vector
#include <algorithm> // needed for find
#include <iostream> // needed for cout, cin
using namespace std;
// Vectors are just like dynamic arrays, you can resize vectors on the fly
vector<int> a { 1,5,4,6,8 }; // Prepare required vector
int v;
cout << "enter value"; // Read from user
cin >> v;
auto itr = find( a.begin(), a.end(), v); // Search entire vector for 'v'
if( itr != a.end() ) // If value entered by user is found in vector
{
a.erase(itr); // Delete the element and shift everything after element
// Toward beginning of vector. This reduces vector size by 1
a.push_back(0); // Add 0 in the end. This increases vector size by 1
}
for( int i : a ) // Iterate through all element of a (i holds element)
cout << i; // Print i
cout << '\n'; // Line end
a few helpful links:
vector , find , iterator , erase , push_back
You could use std::rotate. I suggest that you use std::vector instead of C arrays and take full advantage of the STL algorithms. Nevertheless, below I'm illustrating two versions one with C arrays and one with std::vector:
Version with C array:
#include <iostream>
#include <algorithm>
int main()
{
int const n = 5;
int a[n] = {1,5,4,6,8};
std::cout << "Enter a Value" << std::endl;
int v;
std::cin >> v;
for(auto i : a) std::cout << i<< " ";
std::cout << std::endl;
auto it = std::find(std::begin(a), std::end(a), v);
if(it != std::end(a)) {
std::rotate(it + 1, it, std::end(a));
a[n - 1] = 0;
}
for(auto i : a) std::cout << i<< " ";
std::cout << std::endl;
return 0;
}
Version with vector:
#include <iostream>
#include <vector>
#include <algorithm>
int main()
{
std::vector<int> a{1,5,4,6,8};
std::cout << "Enter a Value" << std::endl;
int v;
std::cin >> v;
for(auto i : a) std::cout << i<< " ";
std::cout << std::endl;
auto it = std::find(std::begin(a), std::end(a), v);
if(it != std::end(a)) {
std::rotate(it + 1, it, std::end(a));
a.back() = 0;
}
for(auto i : a) std::cout << i<< " ";
std::cout << std::endl;
return 0;
}
Here's an example using std::array
#include <array>
#include <algorithm>
// defines our array.
std::array<int, 5> a = {{ 1, 2, 3, 4, 5 }};
// find the position of the element with the value 4.
auto where = std::find(a.begin(), a.end(), 4);
// if it wasn't found, give up
if (where == a.end())
return 0;
// move every element past "where" down one.
std::move(where + 1, a.end(), where);
// fill the very last element of the array with zero
a[ a.size() - 1] = 0;
// loop over our array, printing it to stdout
for (int i : a)
std::cout << i << " ";
std::cout << "\n";
Why would anyone use these awkward algorithms? Well, there are a few reasons. Firstly, they are container-independant. This will work with arrays and vectors and deques, no problem. Secondly, they can be easily used to work with a whole range of elements at once, not just single items, and can copy between containers and so on. They're also type-independant... you acn have an array of strings, or an vector of ints, or other more complex things, and the algorithms will still work just fine.
They're quite powerful, once you've got over their initial user-unfriendliness.
You can always use either std::array or std::vector or whatever without using the standard library algorithms, of course.
std::array<int, 5> a = {{ 1, 2, 3, 4, 5 }};
size_t where = 0;
int to_remove = 4;
// scan through until we find our value.
while (a[where] != to_remove && where < a.size())
where++;
// if we didn't find it, give up
if (where == a.size())
return 0;
// shuffle down the values
for (size_t i = where; i < a.size() - 1; i++)
a[i] = a[i + 1];
// set the last element to zero
a[ a.size() - 1] = 0;
As a final example, you can use memmove (as suggested by BLUEPIXY) to do the shuffling-down operation in one function call:
#include <cstring>
if (where < a.size() - 1)
memmove(&a[where], &a[where + 1], a.size() - where);