new_contents: """Leetcode 111. Minimum Depth of Binary Tree
  Easy
  
  URL: https://leetcode.com/problems/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.
  
  Note: A leaf is a node with no children.
  
  Example:
  Given binary tree [3,9,20,null,null,15,7],
  
      3
     / \
    9  20
      /  \
     15   7
  return its minimum depth = 2.
  """
  
  # Definition for a binary tree node.
  class TreeNode(object):
      def __init__(self, x):
          self.val = x
          self.left = None
          self.right = None
  
  
  class Solution(object):
      def minDepth(self, root):
          """
          :type root: TreeNode
          :rtype: int
          """
          pass
  
  
  def main():
      pass
  
  
  if __name__ == '__main__':
      main()
  
subject: Add lc0111_minimum_depth_of_binary_tree.py