PathSum.ts

// Source : https://leetcode.com/problems/path-sum/
// Author : squxq
// Date   : 2023-11-13

/*****************************************************************************************************
 *
 * Given the root of a binary tree and an integer targetSum, return true if the tree has a
 * root-to-leaf path such that adding up all the values along the path equals targetSum.
 *
 * A leaf is a node with no children.
 *
 * Example 1:
 *
 * Input: root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
 * Output: true
 * Explanation: The root-to-leaf path with the target sum is shown.
 *
 * Example 2:
 *
 * Input: root = [1,2,3], targetSum = 5
 * Output: false
 * Explanation: There two root-to-leaf paths in the tree:
 * (1 --> 2): The sum is 3.
 * (1 --> 3): The sum is 4.
 * There is no root-to-leaf path with sum = 5.
 *
 * Example 3:
 *
 * Input: root = [], targetSum = 0
 * Output: false
 * Explanation: Since the tree is empty, there are no root-to-leaf paths.
 *
 * Constraints:
 *
 * 	The number of nodes in the tree is in the range [0, 5000].
 * 	-1000 <= Node.val <= 1000
 * 	-1000 <= targetSum <= 1000
 ******************************************************************************************************/

export type BT = NodeTree | null;

export class NodeTree {
  val: number;
  left: BT;
  right: BT;
  constructor(val?: number, left?: BT, right?: BT) {
    this.val = val ?? 0;
    this.left = left === undefined ? null : left;
    this.right = right === undefined ? null : right;
  }
}

export function hasPathSum(root: BT, targetSum: number): boolean {
  if (root === null) {
    return false;
  }
  targetSum -= root.val;
  if (root.left === null && root.right === null && targetSum === 0) {
    return true;
  }
  return hasPathSum(root.left, targetSum) || hasPathSum(root.right, targetSum);
}