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Minimum Depth of Binary Tree

Question​

What is the minimum depth of a given binary tree?

Example 1
Input: 
      3
     / \
    9  20
      /  \
     15   7

Output: 2

Solution​

all//Minimum Depth of Binary Tree.py


# Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

class Solution:
    def minDepth(self, root):
        if root is None:
            return 0
        elif root.left is None and root.right is None:
            return 1
        elif root.left is None:
            return self.minDepth(root.right) + 1
        elif root.right is None:
            return self.minDepth(root.left) + 1
        else:
            return min(self.minDepth(root.left), self.minDepth(root.right)) + 1