LeetCode 03: Longest Substring Without Repeating Characters

function lengthOfLongestSubstring(s: string): number {
    let start = 0, len = 0;
    const charMap = new Map<string, number>();

    for (let i = 0; i < s.length; i++) {
        const char = s.charAt(i);

        if (charMap.has(char)) {
            if (charMap.get(char)! >= start) {
                start = charMap.get(char)! + 1;
            }
        }

        len = Math.max(len, i - start + 1);
        charMap.set(char, i);
    }

    return len;
};