index.ts

// HELP:

export function minWindow(S: string, T: string) {
  const HASH = Array(128).fill(0)
  let [left, right, head] = [0, 0, 0]
  let minLength = Infinity
  let counter = T.length

  for (let c of T) HASH[c.charCodeAt(0)]++

  while (right < S.length) {
    if (HASH[S.charCodeAt(right)] > 0) counter--
    HASH[S.charCodeAt(right)]--
    right++

    while (counter === 0) {
      if (right - left < minLength) {
        head = left
        minLength = right - left
      }
      if (HASH[S.charCodeAt(left)] === 0) counter++
      HASH[S.charCodeAt(left)]++
      left++
    }
  }

  return minLength === Infinity ? '' : S.slice(head, head + minLength)
}