Codeforces Round #354 (Div. 2)_Vasya and String(尺取法)

题目连接：http://codeforces.com/contest/676/problem/C

题意：一串字符串，最多改变k次，求最大的相同子串

题解：很明显直接尺取法

#include<cstdio>
#include<cstring>
#include<cmath>
#include<string>
#include<set>
#include<map>
#include<vector>
#include<queue>
#include<algorithm>
#include<functional>
#define cl(a,b) memset(a,b,sizeof(a));
#define FFC(i,a,b) for(int i=a;i<=b;++i)
#define pb push_back
#define LL long long
#define dbg puts("ok")
#define min(a,b) ((a)>(b)?(b):(a))
#define max(a,b) ((a)>(b)?(a):(b))
using namespace std;
char a[100010];
int main(){
    int n,k;
    while(~scanf("%d%d",&n,&k)){
        scanf("%s",a);
        int l=0,r=0,ans=0,ca=0,cb=0,tmp=0;
        while(r<n){
            while(r<n&&tmp<=k){
                if(a[r]=='a')ca++;else cb++;
                tmp=min(ca,cb);
                r++;
            }
            if(r==n&&tmp<=k){ans=max(r-l,ans);break;}
            r--;if(a[r]=='a')ca--;else cb--;tmp=min(ca,cb);
            ans=max(r-l,ans);
            while(a[l]==a[l+1]){if(a[l]=='a')ca--;else cb--;l++,tmp=min(ca,cb);}
                if(a[l]=='a')ca--;else cb--;l++,tmp=min(ca,cb);
        }
        printf("%d
",ans);
    }
    return 0;
}