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[];
 void solve() {
     scanf("%d%d",&k,&n);
     siji(i,,k) {scanf("%d",&pri[i]);s.insert(pri[i]);}
     siji(i,,k){
         set<int>::iterator k=s.begin();
         while() {
             int tm=(*k)*pri[i];
             if(tm<) 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();
 }