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 = 2Output:     1      \       2

Example 2:

Input:     3   / \  0   4   \    2   /  1  L = 1  R = 3Output:       3     /    2     / 1

分析

树的递归遍历

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;    }};