JavaScript刷LeetCode -- 865. Smallest Subtree with all the Deepest Nodes [Medium]

一、题目

  Given a binary tree rooted at root, the depth of each node is the shortest distance to the root.

  A node is deepest if it has the largest depth possible among any node in the entire tree.

  The subtree of a node is that node, plus the set of all descendants of that node.

  Return the node with the largest depth such that it contains all the deepest nodes in its subtree.

二、题目大意

  找出包含所有最深节点的根节点，最深节点的定义：该节点距离二叉树根节点的距离最长。

三、解题思路

  首先找最深节点的问题可以转化为求解二叉树高度的问题，有了高度信息之后，就会产生以下两种情况：

• 当前根节点的左右子树一样高，那么就返回当前根节点。
• 当前根节点的左右子树不一样高，那么返回相对较高的子树的根节点。

  经过递归处理之后，得到最终的答案。

四、代码实现

const subtreeWithAllDeepest = root => {

  return help(root)[1]

  function help (root) {
    if (!root) {
      return [-1, null]
    }
    const l = help(root.left)
    const r = help(root.right)

    const lHeight = l[0]
    const rHeight = r[0]

    const h = Math.max(rHeight, lHeight) + 1

    const v = lHeight === rHeight ? root : (lHeight > rHeight ? l[1] : r[1])

    return [h, v]
  }
}

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