003 Longest Substring Without Repeating Characters 最长不重复子串

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.

详见：https://leetcode.com/problems/longest-substring-without-repeating-characters/description/

Java实现：

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int[] hash=new int[256];
        for(int i=0;i<256;++i){
            hash[i]=-1;
        }
        int maxLen=0;
        int start=-1;
        for(int i=0;i<s.length();++i){
            if(hash[s.charAt(i)]>start){
                start=hash[s.charAt(i)];
            }
            hash[s.charAt(i)]=i;
            maxLen=Math.max(maxLen,i-start);
        }
        return maxLen;
    }
}

python实现：

方法一：

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        start,ans,d=0,0,{}
        for i in range(len(s)):
            c=s[i]
            if c in d and d[c]>=start:
                start=d[c]+1
            else:
                ans=max(ans,i-start+1)
            d[c]=i

        return ans

方法二：

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        ans, l, check = 0, 0, set()
        for i in range(len(s)):
            if s[i] in check:
                while l<i and s[i] in check:
                    check.discard(s[l])
                    l+=1
            check.add(s[i])
            ans=max(ans,len(check))

        return ans