UVa 136 - Ugly Numbers, https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=72

uva-136.cpp

#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <list>
#include <algorithm>
#include <string.h>
#include <string>
#include <queue>
#include <stack>
#include <math.h>
#include <set>

#define FIND 1500

// 2, 3, 5
// 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, ...

int main(void) {

    
    int m[1501];
    
    int pos = 0;
    m[pos] = 1;
    
    while(pos < FIND) {
        int p2 = 0, p3 = 0, p5 = 0;
        
        while(m[pos] >= m[p2] * 2) ++p2;
        while(m[pos] >= m[p3] * 3) ++p3;
        while(m[pos] >= m[p5] * 5) ++p5;

        ++pos;
        
        if(m[pos-1] < m[p2] * 2) m[pos] = m[p2] * 2;
        if(m[pos-1] < m[p3] * 3 && m[pos] > m[p3] * 3) m[pos] = m[p3] * 3;
        if(m[pos-1] < m[p5] * 5 && m[pos] > m[p5] * 5) m[pos] = m[p5] * 5;
        
    }
    
    /*
    for(int i=0; i<FIND; ++i) {
        printf("%d\n", m[i]);
    }*/
    
    printf("The %d'th ugly number is %d.\n", FIND, m[pos - 1]);    
    return EXIT_SUCCESS;
}