Problem Description

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.

Java:

class Solution {
    public int lengthOfLongestSubstring(String s) {
        char[] cs = s.toCharArray();
        HashMap<Character, Integer> map = new HashMap<>();
        int maxLen = 0;
        
        for (int i = 0, pi = -1; i < cs.length; i++) {
            if (map.containsKey(cs[i])) {
                int preCI = map.get(cs[i]);
                while(++pi < preCI) {
                    map.remove(cs[pi]);
                }
            }
            map.put(cs[i], i);
            maxLen = Math.max(i - pi, maxLen);
        }
        return maxLen;
    }
}

Python:

class Solution:
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        dic = {}
        maxLen, pi = 0, -1
        
        for i, c in enumerate(s):
            if dic.get(c, -1) != -1:
                preCI = dic[c]
                while pi < preCI:
                    pi += 1
                    dic[pi] = -1
                    
            dic[c] = i
            maxLen = max(maxLen, i - pi)

        return maxLen

Go:

func lengthOfLongestSubstring(s string) int {
    dic := make(map[rune]int)
    cs := []rune(s)
    pi, maxLen := -1, 0
    
    for i, c := range(cs) {
        if pci, ok := dic[c]; ok {
            for pi < pci {
                pi++
                delete(dic, cs[pi])
            }
        }
        dic[c] = i
        if i - pi > maxLen {
            maxLen = i - pi
        }
    }
        
    return maxLen
}