Largest Substring Between Two Equal Characters - LeetCode javascript solutions

Problem

Given a string s, return the length of the longest substring between two equal characters, excluding the two characters. If there is no such substring return -1.

A substring is a contiguous sequence of characters within a string.

Example 1:

Input: s = "aa"
Output: 0
Explanation: The optimal substring here is an empty substring between the two 'a's.

Example 2:

Input: s = "abca"
Output: 2
Explanation: The optimal substring here is "bc".

Example 3:

Input: s = "cbzxy"
Output: -1
Explanation: There are no characters that appear twice in s.

Constraints:

1 <= s.length <= 300
s contains only lowercase English letters.

Solution

/**
 * @param {string} s
 * @return {number}
 */
var maxLengthBetweenEqualCharacters = function(s) {
    var leftPosMap = Array(26);
    var rightPosMap = Array(26);
    var a = 'a'.charCodeAt(0);
    for (var i = 0; i < s.length; i++) {
        var j = s[i].charCodeAt(0) - a;
        if (leftPosMap[j] === undefined) leftPosMap[j] = i;
        rightPosMap[j] = i;
    }
    var max = -1;
    for (var m = 0; m < 26; m++) {
        if (leftPosMap[m] !== rightPosMap[m]) {
            max = Math.max(max, rightPosMap[m] - leftPosMap[m] - 1);
        }
    }
    return max;
};

Explain:

nope.

Complexity:

Time complexity : O(n).
Space complexity : O(1).