Codeforces Round #354 (Div. 2)-C. Vasya and String

原题链接

维护字符'a'和'b'个数的前缀和num[0][], 和num[1][]。遍历字符串ch[]，若遇到字符ch[j] == 'a,，则用二分查找在num[0]中找到第一个i,时num[0][i]-num[0[j]]+1 > k, 则ans = max(ans, i - j), 在用二分查找在num[1]中找到第一个i使num[1][i]-num[1][j]>k, 则ans = max(ans, i-j);

若遇到字符ch[j] == 'b',同理.

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
#include <stack>
#include <queue> 
#include <cmath>
#include <algorithm>
#define maxn 100005
#define INF 1e9
typedef long long ll;
using namespace std;

int num[2][maxn];
char ch[maxn];
int main(){
	
//	freopen("in.txt", "r", stdin);
	int n, k;
	
	scanf("%d%d%s", &n, &k, ch);
	num[ch[0]-'a'][0] = 1;
	for(int i = 1; i < n; i++){
		int d = ch[i] - 'a';
		num[d^1][i] = num[d^1][i-1];
		num[d][i] = num[d][i-1] + 1;
	}
	int ans = 0;
	for(int i = 0; i < n; i++){
		int d = ch[i] - 'a';
		int l = i, r = n;
		while(l < r){
			int mid = (l + r) >> 1;
			if(num[d^1][mid] - num[d^1][i] <= k)
			  l = mid + 1;
			else
			 r = mid; 
		}
		ans = max(ans, l - i);
		l = i, r = n;
		while(l < r){
			int mid = (l + r) >> 1;
			if(num[d][mid] - num[d][i] + 1 <= k)
			 l = mid + 1;
			else
			 r = mid;
		}
		ans = max(ans, l - i);
	}
	cout << ans << endl;

    return 0;
}</span>

C. Vasya and String

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

High school student Vasya got a string of length n as a birthday present. This string consists of letters 'a' and 'b' only. Vasya denotesbeauty of the string as the maximum length of a substring (consecutive subsequence) consisting of equal letters.

Vasya can change no more than k characters of the original string. What is the maximum beauty of the string he can achieve?

Input

The first line of the input contains two integers n and k (1 ≤ n ≤ 100 000, 0 ≤ k ≤ n) — the length of the string and the maximum number of characters to change.

The second line contains the string, consisting of letters 'a' and 'b' only.

Output

Print the only integer — the maximum beauty of the string Vasya can achieve by changing no more than k characters.

Examples

input

4 2
abba

output

4

input

8 1
aabaabaa

output

5

Note

In the first sample, Vasya can obtain both strings "aaaa" and "bbbb".

In the second sample, the optimal answer is obtained with the string "aaaaabaa" or with the string "aabaaaaa".