题目

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

Example 1:

Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Constraints:

0 <= s.length <= 5 * 104
s consists of English letters, digits, symbols and spaces.

 

思路

解法（Java）

class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s == null || s.length() == 0) return 0;
        Map<Character, Integer> map = new HashMap<>();
        int left = 0, right = 0, len = 1;
        for(int i = 0; i < s.length(); i++){
            char ch = s.charAt(i);
            if(map.containsKey(ch)){
                // 对left的更新
                left = Math.max(left, map.get(ch)+1);
            } 
            map.put(ch, i);
            len = Math.max(len, right-left+1);
            right++;
        }
        return len;
    }
}