QFUN | Editorial by coderag

This problem can be solved using Substrings counting for a given string.  The question is pretty straight forward.  You have to count the number of substrings that start with 0 and end with 1 and the substrings that start with 1 and end with 0. Instead of solving this problem directly, we can count all other types of substrings (starting and ending with 0 and starting and ending with 1) that will be formed in the given string and subtract it with the total substrings that can be formed from the given string.
This will give us the required number of substrings.

We can find the total number of substrings for a given string using the formula `n*(n+1)/2` where n is the length of the string.

The number of substrings that start and end with 1 can be found using `m*(m+1)/2` where m is the number of ones in the given string.

Similarly, we can find the number of substrings that start and end with 0.  Finally, we can print the difference between the total number of substrings and the sum of substrings that start and end with 0 and 1.

```
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
void solve() {
	ll n,z=0,o=0;
	string s;
	cin>>n;
	cin>>s;
	for(char c:s) {
		c=='0'?z++:o++;
	}
	ll t = (n*(n+1))/2;
	z = (z*(z+1))/2;
	o = (o*(o+1))/2;
	cout<<t-(z+o)<<"\n";
}
int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);
	int test;
	cin>>test;
	while(test--) {
		solve();
	}
}

```

QFUN | Editorial by coderag

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