题目描述
题目链接:129. 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 number123
.Find the total sum of all root-to-leaf numbers.
例子
例子 1
Input:
[1,2,3]
Output:25
Explanation:The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.
例子 2
Input:
[4,9,0,5,1]
Output:1026
Explanation:The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.
Note
A leaf is a node with no children.
解题思路
采用 dfs 遍历二叉树,传入当前路径的和,执行以下操作:
- 如果节点为空,直接返回
- 否则,将当前值先乘 10,再加上当前节点值
- 如果当前节点是叶节点,则将当前路径和加入结果中
- 否则对左右子树递归执行操作
代码如下:
class Solution {
public:
int sumNumbers(TreeNode* root) {
int result = 0;
dfs(root, 0, result);
return result;
}
private:
void dfs(TreeNode* root, int current_sum, int& result) {
if (!root) return;
current_sum *= 10;
current_sum += root->val;
if (!root->left && !root->right) {
result += current_sum;
}
dfs(root->left, current_sum, result);
dfs(root->right, current_sum, result);
}
};
- 时间复杂度: O(n)
- 空间复杂度: O(h)
GitHub 代码同步地址: 129.SumRootToLeafNumbers.cpp
其他题目: GitHub: Leetcode-C++-Solution 博客: Leetcode-Solutions