Easy - Sum Root to Leaf Numbers

https://leetcode.com/problems/sum-root-to-leaf-numbers/description

Answer

class TreeNode {
	val: number;
	left: TreeNode | null;
	right: TreeNode | null;

	constructor(val: number = 0, left: TreeNode | null = null, right: TreeNode | null = null) {
		this.val = val;
		this.left = left;
		this.right = right;
	}
}

function sumNumbers(root: TreeNode | null): number {
	function dfs(node: TreeNode | null, currentSum: number): number {
		if (!node) return 0;

		currentSum = currentSum * 10 + node.val;

		if (!node.left && !node.right) { // Check if leaf node
			return currentSum;
		}

		return dfs(node.left, currentSum) + dfs(node.right, currentSum);
	}
	
	return dfs(root, 0);
}