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.

解題

Runtime: 0 ms, faster than 100%

Memory Usage: 2.2 MB, less than 77.70%

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumNumbers(root *TreeNode) int {
   return helper(root, 0)
}

func helper(root *TreeNode, sum int) int {
    if root == nil { return 0 }

    if root.Right == nil && root.Left == nil {
        return sum*10 + root.Val
    }

    lsum := helper(root.Left, sum*10 + root.Val)
    rsum := helper(root.Right, sum*10 + root.Val)


    return  lsum + rsum
}