# Lowest common ancestor (LCA) for Binary Tree and BST

For binary tree, to find the LCA, need to check for the node matching.&#x20;

```java
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (root == null) {
            return null;
        }
        if (root.val == p.val || root.val == q.val) {
            return root;
        } 
        
        TreeNode leftResult = lowestCommonAncestor(root.left, p, q);
        TreeNode rightResult = lowestCommonAncestor(root.right, p, q);

        if (leftResult != null && rightResult != null) {
            return root;
        }

        return leftResult != null ? leftResult : rightResult;
    }
}
```



For BST, it's more efficient to find the node

```java
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (p.val > q.val) {
            return lowestCommonAncestor(root, q, p);
        }
        if (root == null || (p.val <= root.val && q.val >= root.val)) {
            return root;
        }
        if (q.val < root.val) {
            return lowestCommonAncestor(root.left, p, q);
        } else {
            return lowestCommonAncestor(root.right, p, q);
        }
    }

}
```
