覆盖子串篇 ​

const minWindow = (s, t) => {
  const [map, m, n] = [new Map(), s.length, t.length]
  if (m < n) return ''
  let [need, minLen] = [n, m + 1]
  let [i, j] = [-1, -1]
  for (const char of t) {
    map.set(char, (map.get(char) || 0) + 1)
  }
  let [l, r] = [0, 0]
  while (r < m) {
    let char = s.charAt(r++)
    let cnt = map.get(char)
    if (cnt != null) {
      map.set(char, cnt - 1)
      if (cnt > 0) need--
    }
    while (need === 0) {
      if (r - l < minLen) {
        minLen = r - l;
        [i, j] = [l, r]
      }
      char = s.charAt(l++)
      cnt = map.get(char)
      if (cnt != null) {
        map.set(char, cnt + 1)
        if (cnt >= 0) need++
      }
    }
  }
  return s.substring(i, j)
}

const checkInclusion = (t, s) => {
  const [map, m, n] = [new Map(), s.length, t.length]
  if (m < n) return false
  let need = n
  for (const char of t) {
    map.set(char, (map.get(char) || 0) + 1)
  }
  let [l, r] = [0, 0]
  while (r < m) {
    let char = s.charAt(r)
    let cnt = map.get(char)
    if (cnt != null) {
      map.set(char, cnt - 1)
      if (cnt > 0) need--
    }
    l = r++ - n
    if (l >= 0) {
      char = s.charAt(l)
      cnt = map.get(char)
      if (cnt != null) {
        map.set(char, cnt + 1)
        if (cnt >= 0) need++
      }
    }
    if (need === 0) return true
  }
  return false
}

const findAnagrams = (s, t) => {
  const [map, m, n] = [new Map(), s.length, t.length]
  if (m < n) return []
  let [ret, need] = [[], n]
  for (const char of t) {
    map.set(char, (map.get(char) || 0) + 1)
  }
  let [l, r] = [0, 0]
  while (r < m) {
    let char = s.charAt(r)
    let cnt = map.get(char)
    if (cnt != null) {
      map.set(char, cnt - 1)
      if (cnt > 0) need--
    }
    l = r++ - n
    if (l >= 0) {
      char = s.charAt(l)
      cnt = map.get(char)
      if (cnt != null) {
        map.set(char, cnt + 1)
        if (cnt >= 0) need++
      }
    }
    if (need === 0) ret.push(l + 1)
  }
  return ret
}