[Leetcode 3] 最长不重复子串 Longest substring without repeating 滑动窗口

【题目】

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

【举例】

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.
【思路】
　　滑动窗口Sliding Window


【代码】

update 8.22：https://www.bilibili.com/video/BV1ub4y1d7Z8
右边指针一直向前，如果遇到已经存在数组的数，证明之前已遍历过（在左边）。ds.containsKey(s.charAt(right))
于是考虑左指针逼近，如果现在的左指针>此数上次出现的位置，不再更新，反之更新指针

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int ans=0;int left=0;
        Map<Character,Integer> ds=new HashMap<>();
        
        for(int right=0;right<s.length();right++){
            if(ds.containsKey(s.charAt(right)))
                left=Math.max(left,ds.get(s.charAt(right))+1);
            ds.put(s.charAt(right),right);
            ans=Math.max(ans,right-left+1);

        }
        return ans;
    }
}

 

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