236. 二叉树的最近公共祖先

class Solution {
	public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
	        if(root==null||root==p||root==q)return root;
	        TreeNode left =  lowestCommonAncestor(root.left, p,q);
	        TreeNode right =  lowestCommonAncestor(root.right, p,q);
	        if(left == null)  return right; 
	        if(right == null) return left;
	        else return root;                             //左边不空 右边不空 则为公共祖先 root

	}
}