129. Sum Root to Leaf Numbers

129. Sum Root to Leaf Numbers

Medium

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:

• 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:

• 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.

Constraints:

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     public $val = null;
 *     public $left = null;
 *     public $right = null;
 *     function __construct($val = 0, $left = null, $right = null) {
 *         $this->val = $val;
 *         $this->left = $left;
 *         $this->right = $right;
 *     }
 * }
 */
class Solution {

    /**
     * @param TreeNode $root
     * @return Integer
     */
    function sumNumbers($root) {
        return $this->sumNumbersRecu($root, 0);
    }

    function sumNumbersRecu($root, $num) {
        if ($root === null) {
            return 0;
        }

        if ($root->left === null && $root->right === null) {
            return $num * 10 + $root->val;
        }

        return $this->sumNumbersRecu($root->left, $num * 10 + $root->val) + $this->sumNumbersRecu($root->right, $num * 10 + $root->val);
    }
}

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