C++ 9-line very simplest recursion code

  • 0

    Idea is simple and self-explanatory as given in the code comments.
    You can get the idea by taking simple examples of tree with 3 elements(or more).

    class Solution {
        TreeNode* trimBST(TreeNode* root, int L, int R) {
                return root;
            // if root is invalid
            if(root->val < L)
                return trimBST(root->right, L, R);
            if(root->val > R)
                return trimBST(root->left, L, R);
            // if root is valid
            root->left = trimBST(root->left, L, R);
            root->right = trimBST(root->right, L, R);
            return root;

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