p129

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LeetCode p129 Sum Root to Leaf Numbers 题解

1.题目：

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

1

/ \
2 3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

题意：

按以上规则计算一个二叉树的和值。

2.解题思路:

递归。

3.代码

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/**
 * 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 sumNumbers(TreeNode root) {
        return dp(root, 0);
	}

	public int dp(TreeNode root, int sum) {
		if (root == null)
			return 0;
		sum = root.val + sum * 10;
		if (root.left == null && root.right == null)
			return sum;
		
		int a=0;
		if (root.left != null)
			a+= dp(root.left, sum);
		if (root.right != null)
			a+= dp(root.right, sum);
		return a;
	}
}

4.一些总结：