CF之Vasya and String

题目：

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.

解答：

是很明显的尺取法，直接用两个指针或者用队列实现即可

代码如下：

#define _CRT_SECURE_NO_WARNINGS#include<iostream>#include<iomanip>#include<string.h>#include<vector>#include<algorithm>#include<set>#include<map>#include<cstdio>#include<string>using namespace std;int max(int a, int b) {return a < b ? b : a;}int main() {int len, k;cin >> len >> k;string str;cin >> str;int sp, se;sp = se = 0;int cnt = 0;int res = 0;while (se < len) {if (str[se] == 'a') {se++;}else {if (cnt < k) {se++;cnt++;}else {res = max(res, se - sp);while (str[sp] != 'b') {sp++;}sp++;se++;}}}res = max(res, se - sp);sp = se = 0;cnt = 0;while (se < len) {if (str[se] == 'b') {se++;}else {if (cnt < k) {se++;cnt++;}else {res = max(res, se - sp);while (str[sp] != 'a') {sp++;}sp++;se++;}}}res = max(res, se - sp);cout << res << endl;//system("pause");}