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 number 123
.
Find the total sum of all root-to-leaf numbers.
Note: A leaf is a node with no children.
Example:
Input: [1,2,3]
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
Example 2:
Input: [4,9,0,5,1]
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
题目链接:https://leetcode-cn.com/problems/sum-root-to-leaf-numbers/
思路
法一:递归
/**
* 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 {
public:
int sumNumbers(TreeNode* root) {
if(!root) return 0;
int res = 0;
pathSum(root, res, 0);
return res;
}
void pathSum(TreeNode* root, int &res, int sum){
if(!root) return;
sum = sum*10 + root->val;
if(!root->left && !root->right){
res += sum;
}else{
pathSum(root->left, res, sum);
pathSum(root->right, res, sum);
}
}
};
总感觉还有更高级的递归写法。。暂时还想不到。
法二:非递归
暂不练习,后面再补。