Balanced Substring

You are given a string s consisting only of characters 0 and 1. A substring [l, r] of s is a string slsl + 1sl + 2… sr, and its length equals to r - l + 1. A substring is called balanced if the number of zeroes (0) equals to the number of ones in this substring.
You have to determine the length of the longest balanced substring of s.
Input
The first line contains n (1 ≤ n ≤ 100000) — the number of characters in s.
The second line contains a string s consisting of exactly n characters. Only characters 0 and 1 can appear in s.
Output
If there is no non-empty balanced substring in s, print 0. Otherwise, print the length of the longest balanced substring.
Examples
Input
8
11010111
Output
4
Input
3
111
Output
0
Note
In the first example you can choose the substring [3, 6]. It is balanced, and its length is 4. Choosing the substring [2, 5] is also possible.
In the second example it’s impossible to find a non-empty balanced substring.
题目大意：给出一个01串，找出连续的一个区间内0的个数和1的个数相等的最长子串

#include 
#include 
#include 
#include 
#include
#include 
using namespace std;
#define INF 0x3f3f3f3f
int n,sum[100100],num[200100],N=100000,m=0;
int main()
{
     
    std::ios::sync_with_stdio(false);
    cin>>n;
    string s;
    cin>>s;
    memset(sum,0,sizeof(sum));
    memset(num,INF,sizeof(num));
    num[N]=0;
    for(int i=1; i<=n; i++)
    {
     
        if(s[i-1]=='1')
            sum[i]=sum[i-1]+1;
        else
            sum[i]=sum[i-1]-1;
        if(num[N+sum[i]]==INF)//未标记过
            num[N+sum[i]]=i;
        else
            m=max(m,i-num[N+sum[i]]);//已标记过，参与计算
    }
    cout<<m<<endl;
    return 0;
}

本人有个小惑：：：：

不知道为什么，我这道题第一次全用long long答案有时会不对；有点不解？？？找了半天的bug
最后全改成int才
之前怕超int常用long long从未出现过意外
欢迎everyone发表看法为弱弱的我解惑~~