Leetcode76最小覆盖子串(滑动窗口解法)

/**
 * @param {string} s
 * @param {string} t
 * @return {string}
 */
var minWindow = function (s, t) {
  let l = 0;
  let r = 0;
  let res = "";
  const m = new Map();
  for (let i = 0; i < t.length; i++) {
    const c = t[i];
    // 放入字典表
    m.set(c, m.has(c) ? m.get(c) + 1 : 1);
  }
  let needType = m.size;
  while (r < s.length) {
    const c = s[r];
    if (m.has(c)) {
      m.set(c, m.get(c) - 1);
      if (m.get(c) === 0) needType -= 1;
    }
    while (needType === 0) {
      const c2 = s[l];
      let newRes = s.slice(l, r + 1);
      if (!res || newRes.length < res.length) res = newRes;
      if (m.has(c2)) {
        m.set(c2, m.get(c2) + 1);
        if (m.get(c2) === 1) needType += 1;
      }
      l++;
    }
    r++;
  }
  return res;
};
​