0112. Path Sum

https://leetcode.com/problems/path-sum

Description

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

Example 2:

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

Example 3:

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

Constraints:

• The number of nodes in the tree is in the range [0, 5000].

• -1000 <= Node.val <= 1000

• -1000 <= targetSum <= 1000

ac

O(n) remember what does leaf mean: root.left == null && root.right == null

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        if (root == null) return false;
        if (root.left == null && root.right == null) return root.val == sum;
        return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
    }    
}