Leetcode Everyday: 340. Longest Substring with At Most K Distinct Characters

jimhust

于 2016-05-18 22:45:01 发布

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本文介绍了一种使用滑动窗口技术解决LeetCode上一道题目的方法：寻找字符串中最长的包含最多k种不同字符的子串。通过两个指针定义窗口边界，并利用数组记录窗口内各字符出现次数。

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https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/

Given a string, find the length of the longest substring T that contains at most k distinct characters.

For example, Given s = “eceba” and k = 2,

T is "ece" which its length is 3

public class Solution {
    public int lengthOfLongestSubstringKDistinct(String s, int k) {
        if(k==0) return 0;
        char[] cArr = s.toCharArray();
        int[] occ = new int[128];
        int start = 0;
        int dis = 0;
        int maxLen = 0;
        for(int i = 0; i<cArr.length; i++){
            if(occ[cArr[i]]==0){
                occ[cArr[i]]++;dis++;
                if(dis>k){
                    while(--occ[cArr[start++]] != 0);
                }
            }else{
                occ[cArr[i]]++;
            }
            if(i-start+1>maxLen) maxLen = i-start+1;
        }
        return maxLen;
    }
}

The idea is to keep a sliding window using two pointers. The first pointer is start, and the second pointer is i. we record how many times does a char occurs in the window. When we encounter a new char and there are k+1 chars in the window, we increase the start pointer and make correspond changes in the occurrence array, util we find some chars occurrence is from 1->0, this means a char has been removed out of the window.

asd