LeetCode algorithm problem 3-- no repeat characters longest substring

Given a string, you find out which does not contain a sub-length of the longest string of repeated characters.

Example 1:

Input: "abcabcbb"
Output: 3
Explanation: Because the longest substring of characters without repetition is "abc", so its length is 3.
Example 2:

Input: "bbbbb"
Output: 1
Explanation: Because the longest substring is repeated characters without "b", so that its length is 1.
Example 3:

Input: "pwwkew"
Output: 3
Explanation: Because the longest sub-string is repeated characters without "wke", so its length is 3.
Please note that your answer must be a substring of length, "pwke" is a sub-sequence, not a substring.

Source: stay button (LeetCode)
link: https: //leetcode-cn.com/problems/longest-substring-without-repeating-characters
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Mind: if S [j] with j have repeating characters' in the [I, j) range, we do not need increasing i. We can skip [i, j '] within the range of all the elements, and i becomes j' + 1.

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int  size,i=0,j,k,max=0;//i=begin j=end
        size = s.size();
        for(j = 0;j<size;j++){
            for(k = i;k<j;k++)
                if(s[k]==s[j]){//这里用hashmap可以更快找到与s[j]重复的位置i;
                    i = k+1;
                    break;
                }
            if(j-i+1 > max)
                max = j-i+1;
        }
        return max;
    }
};