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
.
思想: 分三种情况: 1. 当前结点为空,返回0. 2. 叶子结点, 返回当前值. 3. 父结点,返回左右两个 path 值的和。
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ int dfs(TreeNode *root, int sum) { if(root == 0) return 0; sum = sum * 10 + root->val; if(root->left || root->right) return dfs(root->left, sum) + dfs(root->right, sum); return sum; } class Solution { public: int sumNumbers(TreeNode *root) { return dfs(root, 0); } };