题解

注意：无子节点的分支不算深度

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    public int run (TreeNode root) {
        if (root == null) {
            return 0;
        }
        int left = 1 + run(root.left);
        int right = 1 + run(root.right);
        if (left == 1 && right == 1) {
            return 1;
        }
        if (left == 1) {
            return right;
        }
        if (right == 1) {
            return left;
        }
        return left < right? left: right;
    }
}