2017/11/7 Leetcode 日记

2017/11/7 Leetcode 日记

669. Trim a Binary Search Tree

Given a binary search tree and the lowest and highest boundaries as L and R, trim the tree so that all its elements lies in [L, R] (R >= L). You might need to change the root of the tree, so the result should return the new root of the trimmed binary search tree.

(修改二叉搜索树，将[L, R]外的节点删除) 

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int L, int R) {
        if(root == NULL) return NULL;
        if(root->val < L) return trimBST(root->right, L, R);
        if(root->val > R) return trimBST(root->left, L, R);
        
        root->left = trimBST(root->left, L, R);
        root->right = trimBST(root->right, L, R);
        return root;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int L, int R, bool top = true) {
        if(root == NULL) return NULL;
        
        root->left = trimBST(root->left, L, R, false);
        root->right = trimBST(root->right, L, R, false);
        
        if(root->val >= L && root->val <= R) return root;
        auto result = root->val < L ? root->right : root->left;
        if(!top) delete root;
        return result;
    }
};