Leetcode/669.TrimaBinarySearchTree.h at master · bluepp/Leetcode · GitHub

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/*
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

*/
    TreeNode* trimBST(TreeNode* root, int L, int R) {

        if (!root) {
            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;
    }