[CF676C]Vasya and String（尺取法，原题）

题目链接：http://codeforces.com/contest/676/problem/C

原题题解链接：http://www.cnblogs.com/vincentX/p/5405468.html

太菜了，昨晚光想着分块，却没考虑做尺取的时候，对于不需要变化的，那对计数器到k不做贡献。早上恍然大悟，5min改出来了…鶸一个。

 /*
 ━━━━━┒ギリギリ♂ eye！
 ┓┏┓┏┓┃キリキリ♂ mind！
 ┛┗┛┗┛┃＼○／
 ┓┏┓┏┓┃ /
 ┛┗┛┗┛┃ノ)
 ┓┏┓┏┓┃
 ┛┗┛┗┛┃
 ┓┏┓┏┓┃
 ┛┗┛┗┛┃
 ┓┏┓┏┓┃
 ┛┗┛┗┛┃
 ┓┏┓┏┓┃
 ┃┃┃┃┃┃
 ┻┻┻┻┻┻
 */
 #include <algorithm>
 #include <iostream>
 #include <iomanip>
 #include <cstring>
 #include <climits>
 #include <complex>
 #include <fstream>
 #include <cassert>
 #include <cstdio>
 #include <bitset>
 #include <vector>
 #include <deque>
 #include <queue>
 #include <stack>
 #include <ctime>
 #include <set>
 #include <map>
 #include <cmath>
 using namespace std;
 #define fr first
 #define sc second
 #define cl clear
 #define BUG puts("here!!!")
 #define W(a) while(a--)
 #define pb(a) push_back(a)
 #define Rint(a) scanf("%d", &a)
 #define Rll(a) scanf("%I64d", &a)
 #define Rs(a) scanf("%s", a)
 #define Cin(a) cin >> a
 #define FRead() freopen("in", "r", stdin)
 #define FWrite() freopen("out", "w", stdout)
 #define Rep(i, len) for(int i = 0; i < (len); i++)
 #define For(i, a, len) for(int i = (a); i < (len); i++)
 #define Cls(a) memset((a), 0, sizeof(a))
 #define Clr(a, x) memset((a), (x), sizeof(a))
 #define Full(a) memset((a), 0x7f7f, sizeof(a))
 #define pi 3.14159265359
 #define RT return
 #define lowbit(x) x & (-x)
 #define onenum(x) __builtin_popcount(x)
 typedef long long LL;
 typedef long double LD;
 typedef unsigned long long ULL;
 typedef pair<int, int> pii;
 typedef pair<string, int> psi;
 typedef map<string, int> msi;
 typedef vector<int> vi;
 typedef vector<LL> vl;
 typedef vector<vl> vvl;
 typedef vector<bool> vb;

 const int maxn = ;
 int n, k;
 int a[maxn];
 char s[maxn];

 int main() {
     // FRead();
     while(~Rint(n) && ~Rint(k)) {
         Rs(s+);
         For(i, , n+) {
             if(s[i] == 'a') a[i] = ;
             else a[i] = ;
         }
         int l = , r = ;
         int cur = , ans = ;
         while() {
             if(r > n) break;
             while(r <= n && cur <= k) {
                 if(a[r] == ) {
                     if(cur == k) break;
                     cur++;
                 }
                 r++;
             }
             if(r - l > ans) ans = r - l;
             while(l <= r && a[l] == ) l++;
             cur--;
             l++;
         }
         int ret = ans;
         For(i, , n+) {
             if(s[i] == 'a') s[i] = 'b';
             else s[i] = 'a';
         }
         For(i, , n+) {
             if(s[i] == 'a') a[i] = ;
             else a[i] = ;
         }
         l = , r = ; cur = , ans = ;
         while() {
             if(r > n) break;
             while(r <= n && cur <= k) {
                 if(a[r] == ) {
                     if(cur == k) break;
                     cur++;
                 }
                 r++;
             }
             if(r - l > ans) ans = r - l;
             while(l <= r && a[l] == ) l++;
             cur--;
             l++;
         }
         printf("%d\n", max(ans, ret));
     }
     RT ;
 }