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.

Analyses: Map each character in the string into a index in an array times, size of that array is from ASCII size. During the process of scanning, update the frequencies of each character. Have a variable count to label how many different characters occur. Whenever the count exceeds k, we know that shorten our range: Let the left pointer move right until the frequency of the character pointed by left is 1.

 1 public class Solution {
 2     public int lengthOfLongestSubstringKDistinct(String s, int k) {
 3         int result = 0, left = 0, n = s.length(), count = 0;
 4         int[] times = new int[256]; // map char in s to a index
 5         for (int right = 0; right < n; right++) {
 6             if (times[s.charAt(right)]++ == 0) count++;
 7             
 8             if (count > k) {
 9                 while (--times[s.charAt(left++)] > 0);
10                 count--;
11             }
12             
13             result = Math.max(result, right - left + 1);
14         }
15         return result;
16     }
17 }

Longest Substring With At Most K Distinct Characters

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