669. 修剪二叉搜索树c

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
struct TreeNode* trimBST(struct TreeNode* root, int low, int high) {
    if(!root) return NULL; 
    if(root->val >= low && root->val <= high){
        root->left=trimBST(root->left,low,high);
        root->right=trimBST(root->right,low,high);
    }else if( root->val < low){
        return trimBST(root->right,low,high);
    }else if(root->val > high){
        return trimBST(root->left,low,high);
    }
    return root;
}