[LeetCode] Longest Substring Without Repeating Characters

Problem

Given a string, find the length of the longest substring without repeating characters.

Examples

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", the answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

很奇怪我为什么没写过这道题...

Solution

class Solution {
    public int lengthOfLongestSubstring(String s) {
        if (s == null || s.length() == 0) return 0;
        Map<Character, Integer> dict = new HashMap<>();
        int start = 0, res = 0;
        for (int i = 0; i < s.length(); i++) {
            Character ch = s.charAt(i);
            Integer pre = dict.get(ch);
            if (pre != null && pre >= start) {
                res = Math.max(res, i - start);
                start = pre + 1;
            }
            dict.put(ch, i);
        }
        return Math.max(s.length()-start, res);
    }
}