写炸了求助，全暴力，想拿5分，但全Re

#include<iostream>
#include<string>
#include<cstring>
#include<map>
using namespace std;
map<string , int> cnt;
string sb,sa,sc;
int yy[90];

int main(){
    int n,m;
    cin>>n>>m;
    for(int i=1;i<=n;++i){
        cin>>sb[i];
    }
    int a,b,c;
    for(int p=1;p<=m;++p){
        int maxn=-1;
        int ml;
        cin>>a>>b;
        c=b-a+1;
        int q=0;
        for(int i=a;i<=b;++i){
            sa[q]=sb[i];
            ++q;
        }
        for (int i = 0; i <c; i++) 
	{
		for (int j = 1+i; j < c; j++)
		{
		    
			sc=sa.substr(i, j - i);
			cnt[sc]++;
			if(cnt[sc]>=maxn){
			maxn=cnt[sc];
			ml=sc.size();
			}
		}
	}
		if(maxn==1)
		cout<<"0"<<endl;
		else
		cout<<ml<<endl;

    }
    return 0;
}