# Lowest Common Ancestor of a Binary Tree II

``````/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
boolean l = check(root, p);
boolean k = check(root, q);
if(!l || !k)
return null;
return find(root, p, q);
}
private boolean check(TreeNode root, TreeNode p) {
if(root == null)
return false;
if(root == p)
return true;
return check(root.left, p) || check(root.right, p);
}

private TreeNode find(TreeNode root, TreeNode p, TreeNode q) {
if (root == null || root == p || root == q)
// found p or q or touch the ground
return root;

// search p and q from left and right
TreeNode left = find(root.left, p, q);
TreeNode right = find(root.right, p, q);

if (left != null && right != null)
// from root's left & right we found both p and q, so root is the LCA
return root;
else
// left is not null means from left's left & right we found both q and q
// so left is the LCA, otherwise, right is the answer
return left != null ? left : right;
}
}``````