leetcode：Minimum Depth Of Binary Tree

没搞懂

1、

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

Given a binary tree as follow:

  1
 / \ 
2   3
   / \
  4   5

The minimum depth is 2.

2、

　　1、递归方式

　　2、不能设置常量，只能在递归中返回该数值

3、

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int minDepth(TreeNode root) {
       if (root == null) {
            return 0;
        }
        return getMin(root);
    }
    public int getMin(TreeNode root) {
        if (root == null) {
            return Integer.MAX_VALUE;
        }

        if (root.left == null && root.right == null) {
            return 1;
        }
　　　　　//递归返回值，逐步加1
        return Math.min(getMin(root.left), getMin(root.right)) + 1;
    }
}