_340_LongestSubstringwithAtMostKDistinctCharacters.java

package leetcode_1To300;

/**
 * 本代码来自 Cspiration，由 @Cspiration 提供
 * 题目来源：http://leetcode.com
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 * - 版权所有，转发请注明出处
 */
public class _340_LongestSubstringwithAtMostKDistinctCharacters {
    /**
     * 340. 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.

     sliding window

     time : O(n)
     space : O(1)

     * @param s
     * @param k
     * @return
     */

    public int lengthOfLongestSubstringKDistinct(String s, int k) {
        int[] count = new int[256];
        int res = 0, num = 0, j = 0;
        for (int i = 0; i < s.length(); i++) {
            if (count[s.charAt(i)]++ == 0) num++;
            if (num > k) {
                while (--count[s.charAt(j++)] > 0);
                num--;
            }
            res = Math.max(res, i - j + 1);
        }
        return res;
    }
}