3. Longest Substring Without Repeating Characters

https://leetcode.com/problems/longest-substring-without-repeating-characters/

JavaScript

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
  var map = {}
  var ans = 0

  for (let i = 0, j = 0; j < s.length; j++) {
    let ch = s[j]

    if (map[ch] !== undefined) {
      i = Math.max(map[ch], i)
    }

    ans = Math.max(ans, j - i + 1)
    map[ch] = j + 1
  }

  return ans
}

Python

class Solution(object):

    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        lookup, ans, i = {}, 0, 0

        for j, c in enumerate(s):
            if c in lookup:
                i = max(lookup[c], i)
            ans = max(ans, j - i + 1)
            lookup[c] = j + 1

        return ans

Go

package main

func lengthOfLongestSubstring(s string) int {
	lookup := make(map[uint8]int)
	answer := 0

	for i, j := 0, 0; j < len(s); j++ {
		ch := s[j]
		_, ok := lookup[ch]

		if ok {
			i = max(lookup[ch], i)
		}

		answer = max(answer, j-i+1)
		lookup[ch] = j + 1
	}

	return answer
}

func max(x int, y int) int {
	if x >= y {
		return x
	}
	return y
}