236. Lowest Common Ancestor of a Binary Tree

 

给定一个二叉树和所要查找的两个节点，找到两个节点的最近公共父亲节点（LCA）。比如，节点5和1的LCA是3，节点5和4的LCA是5。

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);//如果p在左子树，则会返回p，否则返回空

        TreeNode right = lowestCommonAncestor(root.right, p, q);//如果q在右子树，则会返回q，否则返回空

        if(left != null && right != null){

            return root;//如果左右都不为空，则root肯定是祖先节点

        }

        return left == null ? right : left;

    }

}