3. Longest Substring Without Repeating Characters

（最长不重复子串）

Medium

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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.

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int max=1;
        if(s.size()==0) return 0;
        for(int i=0;i<s.size();i++){
            string str=s.substr(i,1);
            int len=1;
            for(int j=i+1;j<s.size();j++){
                if(str.find(s[j])==-1){
                    len++;
                    if(len>max) max=len;
                    str+=s[j];
                }
                else{
                    if(len>max) max=len;
                    j=s.size();
                }
            }
        } 
        return max;
    }
};

• Runtime: 84 ms, faster than 15.11% of C++ online submissions for Longest Substring Without Repeating Characters.
• Memory Usage: 21.5 MB, less than 11.94% of C++ online submissions for Longest Substring Without Repeating Characters.
• Next challenges:
• Longest Substring with At Most Two Distinct Characters
• Longest Substring with At Most K Distinct Characters
• Subarrays with K Different Integers
• 如果设二维数组存储dp[i][j]：字符串 i 到 j 位置的最大值，会内存不够。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int max=1;
        if(s.size()==0) return 0;
        string str=s.substr(0,1);
        int left=0,right=1;
        while(left<s.size() && right<s.size()){
            int f=str.find(s[right]);
            if(f==-1){
                str+=s[right];
                right++;
                if(right-left>max) max=right-left;
            }else{  
                if(right-left>max) max=right-left;
                left=f+left+1;right++;
                str=s.substr(left,right-left);
            }
        }
        return max;
    }
};

• Runtime: 16 ms, faster than 71.44% of C++ online submissions for Longest Substring Without Repeating Characters.
• Memory Usage: 13.9 MB, less than 25.87% of C++ online submissions for Longest Substring Without Repeating Characters.