【LeetCode】111.Minimum Depth of Binary Tree

题目：

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.
解答：
数深度相关问题用递归方式很好解决，递归公式为：minDepth(root) = 1 + min(minDepth(root.left),minDepth(root.right))；

要注意处理单子节点的结点，返回值就不能按照上述公式来了，而应该是1+minDepth(root.notEmptyChild)

/**
* Definition for binary tree
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int minDepth(TreeNode root) {
if(root == null)
return 0;
else if(root.left == null && root.right == null)
return 1;
else if(root.left == null)
return 1 + minDepth(root.right);
else if(root.right == null)
return 1 + minDepth(root.left);
else
return 1 + Math.min(minDepth(root.left), minDepth(root.right));
}
}