P1113:RO

Source #691261:
#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
int main()
{
    int n,k;
    scanf("%d %d",&n,&k);
    char str[n+10];
    scanf("%s", str);

    map<ll,int> qsmap; //pair of {qsvalue,minindex}
    qsmap.insert({0,-1 });
    ll sum = 0;
    int ans = 0;
//  printf("-1 ");for(int i = 0 ; str[i] != '\0' ; i ++)printf("%d ",i);printf("\n 0 ");

    for(int i = 0 ; str[i] != '\0' ; i ++){
        if(str[i] == 'O')sum --;
        else sum += k;
    //  printf("%d ",sum);
        if(qsmap.count(sum) == 0)qsmap.insert({sum,i});
        std::map<ll,int>::iterator its;
        its = qsmap.find(sum);
        if(its != qsmap.end()){
            ans = max(ans,i - its->second);
        }
    }
    printf("%d",ans);
    return 0;
}