G - Ugly Numbers

https://vjudge.net/contest/240386#problem/G

Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, ...
shows the first 11 ugly numbers. By convention, 1 is included. Write a program to find and print the 1500’th ugly number.

Input

There is no input to this program.

Output

Output should consist of a single line as shown below, with ‘<number>’ replaced by the number computed. Sample Output The 1500'th ugly number is <number>.

一步一步改进的代码

第一次（WA）

#include <iostream>
#include <string>
#include <stdio.h>
#include <algorithm>
#include <set>
#include <vector>
#define maxn 1e5+10

using namespace std;

set<long int> s;
vector<int> v;

int main()
{
    long int i,c=0;

    set<long int>::iterator it1;
    s.insert(1);
    for(i=1;;++i)
    {
        if(s.size()>=1500) break;
        it1=s.find(i);
        if(it1!=s.end())
        {
            s.insert(i*2);
            s.insert(i*3);
            s.insert(i*5);
        }
    }

    set<long int>::iterator it;
    it=s.begin();
    for(i=1;i<=1499;++i)
        it++;
        printf("The 1500'th ugly number is %d.\n",(*it));

    return 0;
}

改进后：（TL）

#include <iostream>
#include <string>
#include <stdio.h>
#include <algorithm>
#include <set>
#include <vector>

using namespace std;

set<long int> s;

long int min(long int a,long int b,long int c)
{
    long int min=a;
    if(min>b) min=b;
    if(min>c) min=c;
    return min;
}

int main()
{
    long int i1,i2,i3,c;
    i1=i2=i3=1;

    s.insert(1);
    while(1)
    {
        if(s.size()==1500) break;
        if(!s.count(i1)) {i1++;continue;}
        if(!s.count(i2)) {i2++;continue;}
        if(!s.count(i3)) {i3++;continue;}
        c=min(i1*2,i2*3,i3*5);
        if(c==i1*2) i1++;
        if(c==i2*3) i2++;
        if(c==i3*5) i3++;
        s.insert(c);
    }

    set<long int>::iterator it;
    it=s.end();
    it--;
    printf("The 1500'th ugly number is %d.\n",(*it));

    return 0;
}

再次改进（AC）：

#include <iostream>
#include <string>
#include <stdio.h>
#include <algorithm>
#include <set>
#include <vector>

using namespace std;

set<long int> s;

long int min(long int a,long int b,long int c)
{
    long int min=a;
    if(min>b) min=b;
    if(min>c) min=c;
    return min;
}

int main()
{
    long int i1,i2,i3,c;
    i1=i2=i3=1;

    s.insert(1);
    set<long int>::iterator it1,it2,it3;
    it1=s.begin();
    it2=s.begin();
    it3=s.begin();
    while(1)
    {
        if(s.size()==1500) break;
        c=min(i1*2,i2*3,i3*5);
        if(c==i1*2) i1=*(++it1);
        if(c==i2*3) i2=*(++it2);
        if(c==i3*5) i3=*(++it3);
        s.insert(c);
    }

    set<long int>::iterator it;
    it=s.end();
    it--;
    printf("The 1500'th ugly number is %d.\n",(*it));
    return 0;
}

路漫漫呀！本质还是思维没考虑全