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.

注意，左边为空的时候，只返回右边的+1，右边为空的时候，只返回左边的+1，只有两边都不为空的时候，才返回两者的最小值+1；

/** * Definition for a binary tree node. * 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;        if(root.left == null && root.right == null) return 1;        int leftdepth = minDepth(root.left);        int rightdepth = minDepth(root.right);        if(leftdepth == 0) return rightdepth+1;        if(rightdepth == 0) return leftdepth+1;        return Math.min(leftdepth, rightdepth)+1;    }}