剑指offer-树中两个节点的最低公共祖先

普通二叉树

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
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);
        return left==null ? right : right==null ? left : root;
    }
}

BST平衡二叉树

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
     public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(root == null) 
            return root;
        if(p.val < root.val && q.val < root.val) 
            return lowestCommonAncestor(root.left,p,q);
        if(p.val > root.val && q.val > root.val) 
            return lowestCommonAncestor(root.right,p,q);
        return root;
    }
}