双指针

双指针好用

#include<bits/stdc++.h>
using namespace std;
int main(){
    int t;
    cin >> t;
    while(t--){
        int n;
        cin >> n;
        string s;
        cin >> s;
        int l=0,r=n-1,ans=0;
        while(l<r){
            if((s[l]=='0'&&s[r]=='1')||(s[l]=='1'&&s[r]=='0')){
                l++;
                r--;
                ans++;
            }
            else{
                break;
            }
        }
        cout << n-ans*2 << "\n";
    }
    return 0;
}