leetcode-404-Sum-of-Left-Leaves

发表于   |  

描述

Find the sum of all left leaves in a given binary tree.

Example:

1
2
3
4
5
6
7
    3
   / \
  9  20
    /  \
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

分析

可以直接用递归的方式解决。在原函数里检查当前节点的左子节点是否为叶子节点，如果是，返回该左子节点的值加上右子节点递归调用的结果；如果不是，对左右子节点分别调用递归函数，返回两者之和。

解决方案1(Java)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int sum = 0;
	public int sumOfLeftLeaves(TreeNode root) {
		if (root == null) {
			return 0;
		}
		if (root.left != null && root.left.left == null && root.left.right == null) {
            return root.left.val + sumOfLeftLeaves(root.right);
        }
        return sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);
	}
}

题目来源