Sum Root to Leaf Numbers-优快云博客

本文链接：https://blog.youkuaiyun.com/jialuyyy/article/details/46355087

本文深入探讨如何通过深度优先搜索算法解决求二叉树根到叶节点路径所代表数字总和的问题。详细解释了递归方法的实现过程，并提供了完整的代码实现。

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Sum Root to Leaf Numbers

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.

This problem is a typical depth-first-search problem. using recursive method to solve the problem.

1. traverse every branch of the tree.

2. add up every sum of each branch.

/**
 * 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 helper(root, 0);
        
    }
    
    private int helper(TreeNode root, int sum) {
        if (root == null)
            return 0;
        //if it is the leaf node, return the final result
        if (root.left == null && root.right == null) {
            return root.val + sum * 10;
        }
        //recurse left subtree and right subtree
        return helper(root.left, root.val + sum * 10) + helper(root.right, root.val + sum * 10);
    }
}