Lowest Common Ancestor of a Binary Tree

思路为：

找到p,q,的节点，利用递归从而找到p,q的共公父节点，返回的父节点即为所求的节点

 public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {        if(root== null) return null;if(root==p) return root;else if(root==q) return root;TreeNode left= lowestCommonAncestor(root.left,p,q);TreeNode right=lowestCommonAncestor(root.right,p,q);if(left!=null&&right!=null) return root;else{return left==null?right:left;}    }