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[];
 int main(){
     int n,k;
     while(~scanf("%d%d",&n,&k)){
         scanf("%s",a);
         int l=,r=,ans=,ca=,cb=,tmp=;
         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+]){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\n",ans);
     }
     return ;
 }