Minimum Depth of Binary Tree

Source

• lintcode: Minimum Depth of Binary Tree

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.

Example
Given a binary tree as follow:

  1
 / \ 
2   3
   / \
  4   5
The minimum depth is 2.

Python

"""
Definition of TreeNode:
class TreeNode:
    def __init__(self, val):
        self.val = val
        self.left, self.right = None, None
"""
class Solution:
    """
    @param root: The root of binary tree.
    @return: An integer
    """ 
    def minDepth(self, root):
        # write your code here
        if root is None:
            return 0

        l = self.minDepth(root.left)
        r = self.minDepth(root.right)
        if l==0:
            return r+1
        if r==0:
            return l+1
        return min(l, r)+1