[LeetCode] Sum Root to Leaf Numbers 求根到叶节点数字之和

 

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.

 

这道求根到叶节点数字之和的题跟之前的求Path Sum 二叉树的路径和很类似，都是利用DFS递归来解，这道题由于不是单纯的把各个节点的数字相加，而是每到一个新的数字，要把原来的数字扩大10倍之后再相加。代码如下：

 

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int sumNumbers(TreeNode *root) {
        return sumNumbersDFS(root, 0);
    }
    int sumNumbersDFS(TreeNode *root, int sum) {
        if (!root) return 0;
        sum = sum * 10 + root->val;
        if (!root->left && !root->right) return sum;
        return sumNumbersDFS(root->left, sum) + sumNumbersDFS(root->right, sum);
    }
};

 

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