leetcode_669

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.

Example 1: Input: 1 / 0 2

L = 1 R = 2

Output: 1 2 Example 2: Input: 3 / 0 4 2 / 1

L = 1 R = 3

Output: 3 / 2 / 1

Solutions

1. recursion

/**
 * 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) return nullptr;
        if (root->val < L)
            return trimBST(root->right, L, R);
        else if (root->val > R)
            return trimBST(root->left, L, R);
        else {
            root->left = trimBST(root->left, L, R);
            root->right = trimBST(root->right, L, R);
        }
        return root;
    }
};

1. iteration