LeetCode in TypeScript

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.

Solution

import { TreeNode } from '../../com_github_leetcode/treenode'

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */
function sumNumbers(root: TreeNode | null): number {
    let sum = 0
    function recurseSum(node: TreeNode | null, curNum: number): void {
        if (node === null) {
            return
        }
        const newNum = 10 * curNum + node.val
        if (node.left === null && node.right === null) {
            sum += newNum
            return
        }
        if (node.left !== null) {
            recurseSum(node.left, newNum)
        }
        if (node.right !== null) {
            recurseSum(node.right, newNum)
        }
    }
    recurseSum(root, 0)
    return sum
}

export { sumNumbers }

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