UVA136 Ugly Numbers

题意

PDF

分析

用堆和集合维护即可。

时间复杂度\(O(1500 \log n)\)

代码

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<set>
#include<map>
#include<queue>
#include<stack>
#include<algorithm>
#include<bitset>
#include<cassert>
#include<ctime>
#include<cstring>
#define rg register
#define il inline
#define co const
template<class T>il T read()
{
    rg T data=0;
    rg int w=1;
    rg char ch=getchar();
    while(!isdigit(ch))
    {
        if(ch=='-')
            w=-1;
        ch=getchar();
    }
    while(isdigit(ch))
    {
        data=data*10+ch-'0';
        ch=getchar();
    }
    return data*w;
}
template<class T>T read(T&x)
{
    return x=read<T>();
}
using namespace std;
typedef long long ll;

co int coef[3]={2,3,5};

int main()
{
//  freopen(".in","r",stdin);
//  freopen(".out","w",stdout);
    priority_queue< ll,vector <ll> ,greater <ll> > pq;
    set <ll> s;
    pq.push(1);
    s.insert(1);
    for(int i=1;;++i)
    {
        ll x=pq.top();
        pq.pop();
        if(i==1500)
        {
            cout<<"The 1500'th ugly number is "<<x<<".\n";
            break;
        }
        for(int j=0;j<3;++j)
        {
            ll y=x*coef[j];
            if(!s.count(y))
            {
                s.insert(y);
                pq.push(y);
            }
        }
    }
    return 0;
}