58.Lowest Common Ancestor of a Binary Tree-二叉树的最近公共祖先

解析：

class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(root == null) return null;
        if(root==p || 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;
        if (left==null) return right;
        return left;
    }
}