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
Approach #1: C++.[recursive]
/**
* 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 == NULL) return 0;
vector<string> sumRoot;
helper(root, sumRoot, "");
int ans = 0;
for (string num : sumRoot)
ans += stoi(num);
return ans;
}
private:
void helper(TreeNode* root, vector<string>& sumRoot, string sum) {
if (root == NULL) return;
if (root->left == NULL && root->right == NULL) {
sum = sum+to_string(root->val);
sumRoot.push_back(sum);
return;
}
helper(root->left, sumRoot, sum+to_string(root->val));
helper(root->right, sumRoot, sum+to_string(root->val));
}
};
Approach #2: Java.[recursive]
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int sumNumbers(TreeNode root) {
return sum(root, 0);
}
private int sum(TreeNode root, int s) {
if (root == null) return 0;
if (root.left == null && root.right == null)
return s*10 + root.val;
return sum(root.left, s*10 + root.val) + sum(root.right, s*10 + root.val);
}
}
Approach #3: Python. [dfs+stack]
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def sumNumbers(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if not root:
return 0
res, stack = 0, [(root, root.val)]
while stack:
node, value = stack.pop()
if node:
if not node.left and not node.right:
res += value
if node.left:
stack.append((node.left, value*10 + node.left.val))
if node.right:
stack.append((node.right, value*10 + node.right.val))
return res