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# 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:**

![](https://assets.leetcode.com/uploads/2021/01/18/pathsum1.jpg)

```
**Input:** root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
**Output:** true
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2021/01/18/pathsum2.jpg)

```
**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`

```java
/**
 * 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);
    }    
}
```