159.Longest-Substring-with-At-Most-Two-Distinct-Characters

159. Longest Substring with At Most Two Distinct Characters

题目地址

题目描述

Given a string s , find the length of the longest substring t that contains at most 2 distinct characters.
Example 1:
Input: "eceba"
Output: 3
Explanation: t is "ece" which its length is 3.
Example 2:
Input: "ccaabbb"
Output: 5
Explanation: t is "aabbb" which its length is 5.

代码

Approach #1 Sliding Window + HashMap

class Solution {
public int lengthOfLongestSubstringTwoDistinct(String s) {
int n = s.length;
if (n < 3) return n;
int left = 0;
int right = 0;
HashMap<Character, Integer> hashmap = new HashMap<Character, Integer>();
int max_len = 2;
while (right < n) {
if (hashmap.size() < 3) {
hashmap.put(s.charAt(right), right++);
}
if (hashmap.size() == 3) {
int del_idx = Collections.min(hashmap.values());
hashmap.remove(s.charAt(del_idx));
left = del_idx + 1;
}
max_len = Math.max(max_len, right - left);
}
return max_len;
}
}