Sum Root To Leaf Numbers Problem


Description

LeetCode Problem 129.

You are given the root of a binary tree containing digits from 0 to 9 only.

Each root-to-leaf path in the tree represents a number.

  • For example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123.

Return the total sum of all root-to-leaf numbers. Test cases are generated so that the answer will fit in a 32-bit integer.

A leaf node is a node with no children.

Example 1:

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Input: root = [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:

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Input: root = [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.

Constraints:

  • The number of nodes in the tree is in the range [1, 1000].
  • 0 <= Node.val <= 9
  • The depth of the tree will not exceed 10.


Sample C++ Code

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class Solution {
public:
    int sumNum(TreeNode* root, int num) {
        if (root == NULL)
            return num;
        int curr = num * 10 + root->val;
        int sum = 0;
        if (root->left != NULL)
            sum += sumNum(root->left, curr);
        if (root->right != NULL)
            sum += sumNum(root->right, curr);
        if ((root->left == NULL) && (root->right == NULL))
            sum += curr;
        return sum;
    }
    int sumNumbers(TreeNode* root) {
        return sumNum(root, 0);
    }
};




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