# 112. Path Sum

[Link](https://leetcode.com/problems/path-sum/)

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

**Note:** A leaf is a node with no children.

**Example:**

Given the below binary tree and `sum = 22`,

```
      5
     / \
    4   8
   /   / \
  11  13  4
 /  \      \
7    2      1
```

return true, as there exist a root-to-leaf path `5->4->11->2` which sum is 22.

**Solution**

假設選取目前節點，縮減sum成 sum-node.val條件的情況下看看左右子樹是否有其中一個可以符合。\
\
1\. 要記得edge case的判斷\
2\. 舉簡單的例子看看是否work\\

T: O(N), 基本上也是每個node都要判斷，左子樹or右子樹的case

```
class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        if(root == null) return false;
        if(root.left == null && root.right == null && root.val == sum){
            return true;
        }
        else{
            return hasPathSum(root.left, sum-root.val) || hasPathSum(root.right, sum-root.val);
        }
        
    }
}
```
