src/main/java/com/fishercoder/solutions/_638.java

package com.fishercoder.solutions;

import java.util.ArrayList;
import java.util.List;

public class _638 {
    public static class Solution1 {
        /**
         * reference: https://leetcode.com/articles/shopping-offers/#approach-1-using-recursion-accepted
         */
        public int shoppingOffers(List<Integer> price, List<List<Integer>> special, List<Integer> needs) {
            return shopping(price, special, needs, 0);
        }

        public int shopping(List<Integer> price, List<List<Integer>> special, List<Integer> needs, int i) {
            if (i == special.size()) {
                return dot(needs, price);
            }
            ArrayList<Integer> clone = new ArrayList(needs);
            int j = 0;
            for (; j < special.get(i).size() - 1; j++) {
                int diff = clone.get(j) - special.get(i).get(j);
                if (diff < 0) {
                    break;
                }
                clone.set(j, diff);
            }
            if (j == special.get(i).size() - 1) {
                return Math.min(special.get(i).get(j) + shopping(price, special, clone, i), shopping(price, special, needs, i + 1));
            } else {
                return shopping(price, special, needs, i + 1);
            }
        }

        public int dot(List<Integer> a, List<Integer> b) {
            int sum = 0;
            for (int i = 0; i < a.size(); i++) {
                sum += a.get(i) * b.get(i);
            }
            return sum;
        }
    }
}