最长连续序列

var longestConsecutive = function (nums) {
  //nums未排序，找出数字连续的最长序列，要求O(n)
  let set = new Set(nums) //数组去重放入set中
  let max_len = 0
  for (let num of set) {
    //遍历集合
    let len = 1
    // 从中心向两边扩散查找
    let left = num - 1,
      right = num + 1
    while (set.has(left)) {
      //找到就删掉，避免重复遍历，导致超时
      set.delete(left)
      left--
      len++
    }
    while (set.has(right)) {
      set.delete(right)
      right++
      len++
    }
    max_len = Math.max(len, max_len)
  }
  return max_len
}