LeetCode-3. Longest Substring Without Repeating Characters

1.题目描述

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.

2.我的分析思路

说实话，这题当时拿到没有什么思路，惭愧。。。

3.其他的思路

看了讨论之后，直接贴出代码吧，中间比较精妙。

方法1：

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        Set<Character> set = new HashSet<>();
        int ans = 0, i = 0, j = 0;
        while (i < n && j < n) {
            // try to extend the range [i, j]
            if (!set.contains(s.charAt(j))){
                set.add(s.charAt(j++));
                ans = Math.max(ans, j - i);
            } else {
                set.remove(s.charAt(i++));
            }
        }
        return ans;
    }
}

方法2：

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length(), ans = 0;
        Map<Character, Integer> map = new HashMap<>(); // current index of character
        // try to extend the range [i, j]
        for (int j = 0, i = 0; j < n; j++) {
            if (map.containsKey(s.charAt(j))) {
                i = Math.max(map.get(s.charAt(j)), i);
            }
            ans = Math.max(ans, j - i + 1);
            map.put(s.charAt(j), j + 1);
        }
        return ans;
    }
}