暑假集训Day9 B(尺取法)

题目链接在这里：Problem - B - Codeforces

尺取法一般用于一个数列中的连续子列的问题，思路有点类似于莫队，是一个很巧妙的算法

#include "bits/stdc++.h"
using namespace std;
const int MAX=1e5+5;
int n,k,ans;
char s[MAX];
int main(){
    freopen ("b.in","r",stdin);
    freopen ("b.out","w",stdout);
    int i,j;
    scanf("%d%d
%s",&n,&k,s+1);
    int low,high,le1,le2;
    low=high=1;le1=le2=0;ans=0;
    while (low<=high && high<=n){
        if (s[high]=='b'){
            le2++;
            if (le2>k){
                while (s[low]=='a' && low<=high) low++; low++;
                le2--;
            }
        }
        ans=max(ans,high-low+1);
        //cout<<low<<' '<<high<<' '<<ans<<endl;
        high++;
    }
    low=high=1;
    while (low<=high && high<=n){
        if (s[high]=='a'){
            le1++;
            if (le1>k){
                while (s[low]=='b' && low<=high) low++; low++;
                le1--;
            }
        }
        ans=max(ans,high-low+1);
        //cout<<low<<' '<<high<<' '<<ans<<endl;
        high++;
    }
    
    printf("%d",ans);
    return 0;
}