leetcode 3 Longest Substring Without Repeating Characters - hello lifer

题干

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.

题解1

class Solution {
public:
    int lengthOfLongestSubstring(string s) 
    {
        int len = s.size();
        unordered_set<char> sub;
        int maxlen = 0, i = 0, j = 0;
        while(i < len && j < len)
        {
            if(sub.find(s[i]) == sub.end())
            {
                sub.insert(s[i++]);
                maxlen = max(maxlen, i - j);
            }
            else
            {
                sub.erase(s[j++]);
            }
        }
        return maxlen;
    }
};

题解2 92.07%

class Solution {
public:
    int lengthOfLongestSubstring(string s) 
    {
        int len = s.size();
        int maxlen = 0;
        vector<int> index(128, 0);
        for(int i=0, j=0; i < len; i++)
        {
            j = max(index[s[i]], j);
            maxlen = max(maxlen, i - j + 1);
            index[s[i]] = i + 1;
        }
        return maxlen;
    }
};