Length of the longest substring with equal 1s and 0s

// C++ program to find the length of
// the longest balanced substring
#include <bits/stdc++.h>
using namespace std;

// Function to check if a string contains
// equal number of one and zeros or not
bool isValid(string p)
{
    int n = p.length();
    int c1 = 0, c0 = 0;

    for (int i = 0; i < n; i++) {
        if (p[i] == '0')
            c0++;
        if (p[i] == '1')
            c1++;
    }

    return (c0 == c1) ? true : false;
}

// Function to find the length of
// the longest balanced substring
int longestSub(string s)
{
    int max_len = 0;
    int n = s.length();

    for (int i = 0; i < n; i++) {
        for (int j = i; j < n; j++) {
            if (isValid(s.substr(i, j - i + 1)) && max_len < j - i + 1)
                max_len = j - i + 1;
        }
    }
    return max_len;
}

// Driver code
int main()
{
    string s = "101001000";

    // Function call
    cout << longestSub(s);

    return 0;
}

// This code is contributed by Aditya Kumar (adityakumar129)

// C++ for finding length of longest balanced
// substring
#include<bits/stdc++.h>
using namespace std;

// Returns length of the longest substring 
// with equal number of zeros and ones.
int stringLen(string str)
{
    // Create a map to store differences
    // between counts of 1s and 0s.
    map<int, int> m;
    
    // Initially difference is 0.
    m[0] = -1;   
    
    int count_0 = 0, count_1 = 0;
    int res = 0;
    for (int i=0; i<str.size(); i++)
    {
        // Keeping track of counts of
        // 0s and 1s.
        if (str[i] == '0')
            count_0++;
        else
            count_1++;
            
        // If difference between current counts
        // already exists, then substring between
        // previous and current index has same
        // no. of 0s and 1s. Update result if this
        // substring is more than current result.
        if (m.find(count_1 - count_0) != m.end())
            res = max(res, i - m[count_1 - count_0]);
            
        // If current difference is seen first time.        
        else
            m[count_1 - count_0] = i;
    }

    return res;
}

// driver function
int main()
{
    string str = "101001000";
    cout << "Length of longest balanced"
            " sub string = ";
    cout << stringLen(str);
    return 0;
}