LeetCode 129: Sum Root to Leaf Numbers

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#leetcode #二叉树 #DFS

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本文介绍了一种解决特定二叉树问题的方法：计算所有从根节点到叶子节点的路径数值之和。通过深度优先搜索策略，递归地计算每个路径的数值，并最终返回所有路径数值的总和。

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.

解题思路

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    void dfs(TreeNode *root, int num, int &sum) {
        if (root == NULL) return;

        num = num * 10 + root->val;
        if (root->left == NULL && root->right == NULL) {
            sum += num;
        }
        else {
            dfs(root->left, num, sum);
            dfs(root->right, num, sum);
        }
    }

public:
    int sumNumbers(TreeNode* root) {
        int sum = 0;
        dfs(root, 0, sum);
        return sum;
    }
};