Sum Root to Leaf Numbers

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#二叉树

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本文详细介绍了如何使用递归算法解决二叉树中从根节点到叶子节点的所有路径数字之和的问题，并提供了具体实现代码。

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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.

计算所有路径的和，从根节点到叶子节点每条路径都代表一个十进制的数字。用递归从根节点开始，依次记录所有路径上组成数字的和。代码如下：


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