424. Longest Repeating Character Replacement

Given a string that consists of only uppercase English letters, you can replace any letter in the string with another letter at most k times. Find the length of a longest substring containing all repeating letters you can get after performing the above operations.

Note:
Both the string's length and k will not exceed 104.

Example 1:

Input:
s = "ABAB", k = 2

Output:
4

Explanation:
Replace the two 'A's with two 'B's or vice versa.

 

Example 2:

Input:
s = "AABABBA", k = 1

Output:
4

Explanation:
Replace the one 'A' in the middle with 'B' and form "AABBBBA".
The substring "BBBB" has the longest repeating letters, which is 4.

此题题目如果能读懂的话,就算成功了,看了答案,大致意思是,遍历整个字符串,当到某一个字符的时候,end-start+1-包含字符个数最多的个数>k时候,把最左面的字符在数组里面出现的次数减一
并且start向右遍历,代码如下:
 1 public class Solution {
 2     public int characterReplacement(String s, int k) {
 3         int start = 0;
 4         int end = 0;
 5         int[] count = new int[26];
 6         int max = 0;
 7         int mainmax = 0;
 8         for(;end<s.length();end++){
 9             mainmax = Math.max(mainmax,++count[s.charAt(end)-'A']);
10             while(end-start-mainmax+1>k){
11                 count[s.charAt(start)-'A']--;
12                 start++;
13             }
14             max = Math.max(max,end-start+1);
15         }
16         return max;
17     }
18 }

此题说白了就是,进行两次比较,一次记录出现字符数目最多的情形,另外一次记录出现的最大长度,while来处理数目大于k的情况。

posted @ 2017-03-06 09:02  CodesKiller  阅读(141)  评论(0编辑  收藏  举报