3. Longest Substring Without Repeating Characters (Medium)

Given a string s, find the length of the longest substring without repeating characters.

Example 1: Input: s = “abcabcbb” Output: 3 Explanation: The answer is “abc”, with the length of 3.

Example 2: Input: s = “bbbbb” Output: 1 Explanation: The answer is “b”, with the length of 1.

Example 3: Input: s = “pwwkew” Output: 3 Explanation: The answer is “wke”, with the length of 3. Notice that the answer must be a substring, “pwke” is a subsequence and not a substring.

Constraints: 0 <= s.length <= 5 * 10^4 s consists of English letters, digits, symbols and spaces.

/**
* @param {string} s
* @return {number}
*/
var lengthOfLongestSubstring = function (s) {
   // Store counters for the the start of the window and the longest string's length
   var startOfWindow = 0,
       longestStringLength = 0;

   // Initialise a Map to store the characters of the current string
   var characterMap = new Map();

   // Loop through the provided string
   for (let i = 0; i < s.length; i++) {
       // Store the current character, and its position in the Map (saves repeatedly looking it up)
       let currentCharacter = s[i];
       let currentCharacterPositionInMap = characterMap.get(currentCharacter);

       // Check if current character exists in the Map, and was found within the current window
       if (currentCharacterPositionInMap >= startOfWindow) {
           // Move the current window to start after the first instance of the current character
           startOfWindow = currentCharacterPositionInMap + 1;
       }

       // Add the current character to the Map with its position in the string
       characterMap.set(currentCharacter, i);

       // Store the current string length if bigger than the existing record
       longestStringLength = Math.max(
           longestStringLength,
           i - startOfWindow + 1
       );
       console.log(characterMap, longestStringLength)
   }

   return longestStringLength;
};

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