【leetcode】3. Longest Substring Without Repeating Characters

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

Example 1:

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

Example 2:

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

Example 3:

Input: "pwwkew"
Output: 3
Explanation: 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.

題解如下：

思路1：

 

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        int ans = 0,i = 0,j = 0;
        Set<Character> set = new HashSet<>();
        while(i < n && j < n) {
            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;
    }
}

思路2：

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        int ans = 0;
        Map<Character,Integer> map = new HashMap<>();
        for(int i = 0,j =0;j < n;j++) {
            if(map.containsKey(s.charAt(j))) {
                i = Math.max(i,map.get(s.charAt(j))+1);//skip
            }
            ans = Math.max(ans,j-i+1);
            map.put(s.charAt(j),j);
        }
        return ans;
    }
}