3. Longest Substring Without Repeating Characters

Posted 2020-11-23 blackyao

3. Longest Substring Without Repeating Characters

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) {
        
        unordered_map<char,int> hash;     
        
        int i=0, j=0;
        int result = 0;
        
        while(j<s.size()) {
            if(hash.count(s[j])>0 && hash[s[j]]>=i) {
                i = hash[s[j]]+1;
            }
            
            result = max(result, j-i+1);
            
            hash[s[j]] = j;
            ++j;
        }
        
        return result;
    }
};