problem

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 are 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

submission

// Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
// 
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }

use std::cell::RefCell;
use std::rc::Rc;

// we could solve this by iteration
// however recursion with pattern matching
// is way easier to impl.
impl Solution {
    pub fn has_path_sum(
        root: Option<Rc<RefCell<TreeNode>>>,
        ts: i32,
    ) -> bool {
        root.map_or_else(
            || false,
            |node| match *node.borrow() {
                TreeNode {
                    val,
                    left: None,
                    right: None,
                } => val == ts,
                TreeNode {
                    val,
                    ref left,
                    ref right,
                } => {
                    Self::has_path_sum(left.clone(), ts - val)
                        || Self::has_path_sum(right.clone(), ts - val)
                }
            },
        )
    }
}