[LeetCode]638. Shopping Offers

https://leetcode.com/problems/shopping-offers/#/description

给每种商品的价格、多组不同offer（每个offer内最后一个为价格，前面为每种商品在这个offer内的数量）、最终要买的个数

要求exactly每个商品给定个数，所需要的最少钱

遍历 + 回溯（递归）

查看每个offer在当前needs下是否valid，如果valid就按照新的needs进行递归

public class Solution {    public int shoppingOffers(List<Integer> price, List<List<Integer>> special, List<Integer> needs) {        int res = Integer.MAX_VALUE;        for (int i = 0; i < special.size(); i++) {        boolean isValid = true;        List<Integer> offer = special.get(i);        for (int j = 0; j < needs.size(); j++) {        int remain = needs.get(j) - offer.get(j);        if (remain < 0) {        isValid = false;        }        needs.set(j, remain);        }        if (isValid) {        res = Math.min(res, shoppingOffers(price, special, needs) + offer.get(needs.size()));        }        for (int j = 0; j < needs.size(); j++) {        needs.set(j, needs.get(j) + offer.get(j));        }        }        int nonOffer = 0;        for (int i = 0; i < needs.size(); i++) {        nonOffer += needs.get(i) * price.get(i);        }        return Math.min(nonOffer, res);    }}