USACO 3.1 Humble Numbers

Humble Numbers

For a given set of K prime numbers S = {p₁, p₂, ..., p_K}, consider the set of all numbers whose prime factors are a subset of S. This set contains, for example, p₁, p₁p₂, p₁p₁, and p₁p₂p₃ (among others). This is the set of `humble numbers' for the input set S. Note: The number 1 is explicitly declared not to be a humble number.

Your job is to find the Nth humble number for a given set S. Long integers (signed 32-bit) will be adequate for all solutions.

PROGRAM NAME: humble

INPUT FORMAT

Line 1:	Two space separated integers: K and N, 1 <= K <=100 and 1 <= N <= 100,000.
Line 2:	K space separated positive integers that comprise the set S.

SAMPLE INPUT (file humble.in)

4 19
2 3 5 7

OUTPUT FORMAT

The Nth humble number from set S printed alone on a line.

SAMPLE OUTPUT (file humble.out)

27

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所以就是一道set的简单应用

然而我的内存在最后一个测试点炸了

事实上操作内存不需要n*k然后第n次的begin，只要不断维护这个序列是n长最后把--end抛出去

然后就没有内存问题了，还会比较快

/*
ID: ivorysi
PROG: humble
LANG: C++
*/
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <set>
#define siji(i,x,y) for(int i=(x);i<=(y);++i)
#define gongzi(j,x,y) for(int j=(x);j>=(y);--j)
#define xiaosiji(i,x,y) for(int i=(x);i<(y);++i)
#define sigongzi(j,x,y) for(int j=(x);j>(y);--j)
#define inf 0x7fffffff
#define MAXN 100005
#define ivorysi
using namespace std;
typedef long long ll;
set<int> s;
int n,k,pri[105];
void solve() {
    scanf("%d%d",&k,&n);
    siji(i,1,k) {scanf("%d",&pri[i]);s.insert(pri[i]);}
    siji(i,1,k){
        set<int>::iterator k=s.begin();
        while(1) {
            int tm=(*k)*pri[i];
            if(tm<0) break;
            if(s.size()>n) {
                s.erase(--s.end());
                if(tm>(*--s.end())) 
                    break;
            }
            s.insert(tm);
            ++k;
        }
    }
    printf("%d\n",*(--s.end()));
}
int main(int argc, char const *argv[])
{
#ifdef ivorysi
    freopen("humble.in","r",stdin);
    freopen("humble.out","w",stdout);
#else
    freopen("f1.in","r",stdin);
#endif
    solve();
}