# Largest subarray with equal number of 0s and 1s in C++

Let's see the steps to complete the program.

• Initialise the array.
• Make all zeroes in the array to -1.
• Have a map an empty map to store the previous indexes.
• Initialise sum to 0, max length to 0 and ending index to -1.
• Write a loop that iterates till n.
• Add current element to sum.
• If the sum is equal to 0.
• Update the max length with i + 1.
• And ending index to i.
• If the sum is present in previous sums map and i - previousIndexes[sum] is greater than max length.
• Update the max length and ending index.
• Else add the sum to the previous indexes map.
• Print the starting index endingIndex - maxLength + 1 and ending index endingIndex.

## Example

Let's see the code.

Live Demo

#include <bits/stdc++.h>
using namespace std;
void findTheSubArray(int arr[], int n) {
unordered_map<int, int> previousIndexes;
int sum = 0, maxLength = 0, endingIndex = -1;
for (int i = 0; i < n; i++) {
arr[i] = arr[i] == 0 ? -1 : 1;
}
for (int i = 0; i < n; i++) {
sum += arr[i];
if (sum == 0) {
maxLength = i + 1;
endingIndex = i;
}
if (previousIndexes.find(sum) != previousIndexes.end()) {
if (maxLength < i - previousIndexes[sum]) {
maxLength = i - previousIndexes[sum];
endingIndex = i;
}
}else {
previousIndexes[sum] = i;
}
}
cout << endingIndex - maxLength + 1 << " " << endingIndex << endl;
}
int main() {
int arr[] = { 1, 1, 0, 0, 0, 1, 1, 1, 0 };
findTheSubArray(arr, 9);
return 0;
}

## Output

If you run the above code, then you will get the following result.

1 8

## Conclusion

If you have any queries in the tutorial, mention them in the comment section.