Leetcode 111. Minimum Depth of Binary Tree

Description:Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. Note: A leaf is a node with no children.

Link: 111. Minimum Depth of Binary Tree

EXamples:

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 2

Example 2:
Input: root = [2,null,3,null,4,null,5,null,6]
Output: 5

思路: 之前计算最深的路径时，是1+max(左子树的最深度，右子树的最深度)，现在求最小深度，即最短路径的节点数，就用1+min(左子树的最小深度，右子树的最小深度)。但是看Example2, 如果没有左子树，最小深度不是1，而是右子树的最小深度5，所以要单独处理。

class Solution(object):
    def minDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root: return 0
        if not root.left:
            return 1 + self.minDepth(root.right)
        elif not root.right:
            return 1 + self.minDepth(root.left)
        else:
            return 1 + min(self.minDepth(root.left), self.minDepth(root.right))

日期: 2021-03-18