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Question

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.

Solution

Result: Accepted Time: 0 ms

Here should be some explanations.

int sum_tree(struct TreeNode* root,int sum)
 {
     if(root == NULL) return 0;
     sum = sum *10 + root->val;
     int ret =  sum_tree(root->left,sum) + sum_tree(root->right,sum);
     return ret==0?sum:ret;
 }

int sumNumbers(struct TreeNode* root) {
    return sum_tree(root,0);
}

Complexity Analytics

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$