[leetcode]669. Trim a Binary Search Tree

[leetcode]669. Trim a Binary Search Tree

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Analysis

ummmm~—— [ummmm~]

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.
参考了大神的做法：如果节点数值在范围内，则递归遍历其左子树和右子树；如果节点数值低于下界，则直接抛弃该节点和其左子树；如果节点数值高于上界，则直接抛弃该节点和其右子树。

Implement

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