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function lengthOfLongestSubstring(s: string): number {
  // Pattern: Sliding Window (Variable Size)
  const charMap = new Map<string, number>();
  let left = 0, maxLen = 0;

  for (let right = 0; right < s.length; right++) {
    if (charMap.has(s[right]))
      // Shrink window from left
      left = Math.max(left, charMap.get(s[right])! + 1);
    charMap.set(s[right], right);
    maxLen = Math.max(maxLen, right - left + 1);
  }
  return maxLen;
}