LDUOJ 1586. 【吴永辉】程序设计基础实践7-9 N. Dollar Dayz

N. Dollar Dayz

题目描述：

Farmer John goes to Dollar Days at The Cow Store and discovers an unlimited number of tools on sale. During his first visit, the tools are selling variously for $1, $2, and $3. Farmer John has exactly $5 to spend. He can buy 5 tools at $1 each or 1 tool at $3 and an additional 1 tool at $2. Of course, there are other combinations for a total of 5 different ways FJ can spend all his money on tools. Here they are:
1 @ US$3 + 1 @ US$2
1 @ US$3 + 2 @ US$1
1 @ US$2 + 3 @ US$1
2 @ US$2 + 1 @ US$1
5 @ US$1Write a program than will compute the number of ways FJ can spend N dollars (1≤N≤1000) at The Cow Store for tools on sale with a cost of $1..$K (1≤K≤100).

给你一定金额n的硬币，再给出k件商品，第i件商品的价格为i。用n金额有多少种购买方案？

输入

A single line with two space-separated integers: N and K.

输出

A single line with a single integer that is the number of unique ways FJ can spend his money.

样例：

Input：
5 3
output：
5

题解报告：

是一个变形的 完全背包问题，而且还是高精度的，用long long 储存种类数也会爆，开两个数组，分别储存大于1e18，和小于1e18的数字；详细过程见代码注释
如若不懂完全背包问题可以学习此视频（针对小白友好）：戳我

附上代码：

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF=1e18;
const int maxn=1001;
ll a[maxn][maxn],b[maxn][maxn];