Lowest Common Ancestor of a Binary Tree(Medium)

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
    //发现目标节点则通过返回值标记该子树发现了某个目标结点
    if(root == null || root == p || root == q) return root;

    //查看左子树中是否有目标结点，没有为null
    TreeNode left = lowestCommonAncestor(root.left, p, q);
    //查看右子树是否有目标节点，没有为null
    TreeNode right = lowestCommonAncestor(root.right, p, q);

    //都不为空，说明做右子树都有目标结点，则公共祖先就是本身
    if(left!=null&&right!=null) return root;
    //如果发现了目标节点，则继续向上标记为该目标节点
    return left == null ? right : left;
}