Path Sum II

Problem statement

Given the root of a binary tree and an integer targetSum, return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path should be returned as a list of the node values, not node references.

A root-to-leaf path is a path starting from the root and ending at any leaf node. A leaf is a node with no children.

Example 1:

Input: root = [5,4,8,11,null,13,4,7,2,null,null,5,1], targetSum = 22Output: [[5,4,11,2],[5,8,4,5]]Explanation: There are two paths whose sum equals targetSum:5 + 4 + 11 + 2 = 225 + 8 + 4 + 5 = 22

Example 2:

Input: root = [1,2,3], targetSum = 5Output: []

Example 3:

Input: root = [1,2], targetSum = 0Output: []

Constraints:

• The number of nodes in the tree is in the range [0, 5000].
• -1000 <= Node.val <= 1000
• -1000 <= targetSum <= 1000

My solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} targetSum
 * @return {number[][]}
 */
var pathSum = function(root, targetSum) {
    const result = [];
    
    function dfs(node, path = []) {
//         base case
        if (!node) {
            return
        }
        if (!node.left && !node.right) {
            // console.log(node, path)
//             leaf node
            path.push(node.val)
            if (sum(path) === targetSum) {
                result.push(path)
            }
//             Exit if this is the lead node
            return;
        }
        
        path.push(node.val)
        
        if (node.left) {
            dfs(node.left, [...path])
        }
        
        if (node.right) {
            dfs(node.right, [...path])
        }
    }
    
    function sum(arr) {
        return arr.reduce((acc, curr) => {
            acc += curr
            return acc;
        }, 0)
    }
    
    dfs(root);
    
    return result;
};