Leetcode•Aug 06, 2025

Minimum Window Substring

Hazrat Ali

Leetcode

The testcases will be generated such that the answer is unique.

 

Example 1:

Input: s = "ADOBECODEBANC", t = "ABC"
Output: "BANC"
Explanation: The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t.

Example 2:

Input: s = "a", t = "a"
Output: "a"
Explanation: The entire string s is the minimum window.

Example 3:

Input: s = "a", t = "aa"
Output: ""
Explanation: Both 'a's from t must be included in the window.
Since the largest window of s only has one 'a', return empty string.

Solution
/**
 * @param {string} s
 * @param {string} t
 * @return {string}
 */
const minWindow = (s, t) => {
 
  const map = {};
  for (let c of t) {
    map[c] = ~~map[c] + 1;
  }

  let start = 0;
  let size = Infinity;
  let counter = t.length;

 
  for (let i = 0, j = 0; j < s.length; j++) {
   
    if (map[s[j]]-- > 0) {
      counter--;
    }

   
    while (counter === 0) {
      if (j - i + 1 < size) {
        size = j - i + 1;
        start = i;
      }

      if (map[s[i++]]++ === 0) {
        counter++;
      }
    }
  }

  return size === Infinity ? '' : s.substr(start, size);
};




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