What I've done today is Last Digits of Number Theory and Longest Substring Without Repeating Characters in JavaScript.

If no source is provided, then I'm doing these challenge at https://brilliant.org and https://leetcode.com/.

Math

On the first view of problem, there comes the answer is three.

Five times an even number is zero, whatever number time zero is zero.

Five times an odd number is five.

Obviously there is loop (2->4->8->6) in the multiply chain.

So obvious~

Algorithm

Problem

3. Longest Substring Without Repeating Characters

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.

Solution

Implementation

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
    let map = new Map();
    let lp = 0;
    let ans = 0;
    let len = s.length;
    for(let i = 0; i < len ; ++i){
        if(map.has(s[i]) && lp < map.get(s[i]) + 1) lp = map.get(s[i]) + 1;
        ans = ans > ( i - lp + 1 ) ? ans : ( i - lp + 1 );
        //console.log(ans,lp)
        map.set(s[i], i);
    }
    return ans;
};

//console.log(lengthOfLongestSubstring("abba"));