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。
1 /* 2 ━━━━━┒ギリギリ♂ eye！ 3 ┓┏┓┏┓┃キリキリ♂ mind！ 4 ┛┗┛┗┛┃＼○／ 5 ┓┏┓┏┓┃ / 6 ┛┗┛┗┛┃ノ) 7 ┓┏┓┏┓┃ 8 ┛┗┛┗┛┃ 9 ┓┏┓┏┓┃ 10 ┛┗┛┗┛┃ 11 ┓┏┓┏┓┃ 12 ┛┗┛┗┛┃ 13 ┓┏┓┏┓┃ 14 ┃┃┃┃┃┃ 15 ┻┻┻┻┻┻ 16 */ 17 #include <algorithm> 18 #include <iostream> 19 #include <iomanip> 20 #include <cstring> 21 #include <climits> 22 #include <complex> 23 #include <fstream> 24 #include <cassert> 25 #include <cstdio> 26 #include <bitset> 27 #include <vector> 28 #include <deque> 29 #include <queue> 30 #include <stack> 31 #include <ctime> 32 #include <set> 33 #include <map> 34 #include <cmath> 35 using namespace std; 36 #define fr first 37 #define sc second 38 #define cl clear 39 #define BUG puts("here!!!") 40 #define W(a) while(a--) 41 #define pb(a) push_back(a) 42 #define Rint(a) scanf("%d", &a) 43 #define Rll(a) scanf("%I64d", &a) 44 #define Rs(a) scanf("%s", a) 45 #define Cin(a) cin >> a 46 #define FRead() freopen("in", "r", stdin) 47 #define FWrite() freopen("out", "w", stdout) 48 #define Rep(i, len) for(int i = 0; i < (len); i++) 49 #define For(i, a, len) for(int i = (a); i < (len); i++) 50 #define Cls(a) memset((a), 0, sizeof(a)) 51 #define Clr(a, x) memset((a), (x), sizeof(a)) 52 #define Full(a) memset((a), 0x7f7f, sizeof(a)) 53 #define pi 3.14159265359 54 #define RT return 55 #define lowbit(x) x & (-x) 56 #define onenum(x) __builtin_popcount(x) 57 typedef long long LL; 58 typedef long double LD; 59 typedef unsigned long long ULL; 60 typedef pair<int, int> pii; 61 typedef pair<string, int> psi; 62 typedef map<string, int> msi; 63 typedef vector<int> vi; 64 typedef vector<LL> vl; 65 typedef vector<vl> vvl; 66 typedef vector<bool> vb; 67 68 const int maxn = 100010; 69 int n, k; 70 int a[maxn]; 71 char s[maxn]; 72 73 int main() { 74 // FRead(); 75 while(~Rint(n) && ~Rint(k)) { 76 Rs(s+1); 77 For(i, 1, n+1) { 78 if(s[i] == 'a') a[i] = 0; 79 else a[i] = 1; 80 } 81 int l = 1, r = 1; 82 int cur = 0, ans = 0; 83 while(1) { 84 if(r > n) break; 85 while(r <= n && cur <= k) { 86 if(a[r] == 0) { 87 if(cur == k) break; 88 cur++; 89 } 90 r++; 91 } 92 if(r - l > ans) ans = r - l; 93 while(l <= r && a[l] == 1) l++; 94 cur--; 95 l++; 96 } 97 int ret = ans; 98 For(i, 1, n+1) { 99 if(s[i] == 'a') s[i] = 'b'; 100 else s[i] = 'a'; 101 } 102 For(i, 1, n+1) { 103 if(s[i] == 'a') a[i] = 0; 104 else a[i] = 1; 105 } 106 l = 1, r = 1; cur = 0, ans = 0; 107 while(1) { 108 if(r > n) break; 109 while(r <= n && cur <= k) { 110 if(a[r] == 0) { 111 if(cur == k) break; 112 cur++; 113 } 114 r++; 115 } 116 if(r - l > ans) ans = r - l; 117 while(l <= r && a[l] == 1) l++; 118 cur--; 119 l++; 120 } 121 printf("%d ", max(ans, ret)); 122 } 123 RT 0; 124 }