丑数

只包含因子2,3,5的数叫丑数，求从小到大顺序的第1500个丑数，例如6,8都是丑数，但14不是。因为它包含因子7。习惯上我们认为1是丑数。

思路：丑数肯定是由丑数*2或3或5生成的。由空间换时间的做法。

#include<iostream>

using namespace std;

int Min(int num1,int num2,int num3){
    int min=(num1 < num2) ?  num1 : num2;
    min=(min < num3) ?  min : num3;
    return min;
    
}
    
int uglyNumber(int index){
    if(index <= 0)        
         return 0;
    
    int *pUglyArray = new int[index];    
  //  memset(pUglyArray,1,sizeof(pUglyArray));
    pUglyArray[0] = 1;
    
    int *p2 = pUglyArray;
    int *p3 = pUglyArray;
    int *p5 = pUglyArray;
    
    int nextIndex = 1;
    while(nextIndex < index){
        int min = Min(*p2*2,*p3*3,*p5*5);        
        pUglyArray[nextIndex] = min;
        while(*p2 * 2 <= pUglyArray[nextIndex])
        p2++;
        while(*p3 * 3 <= pUglyArray[nextIndex])
        p3++;
        while(*p5 * 5 <= pUglyArray[nextIndex])
        p5++;      
                    
                    
        nextIndex++;                
    }
    
    int ugly=pUglyArray[nextIndex-1];
    
    for(int i = 0; i < index; i++){
          cout<<pUglyArray[i]<<" ";        
    }                                                                                                                                                                                       
    
     delete[] pUglyArray;
   
   
   return ugly;    
    
    
}    
    
int main(){
    int index = 10;
    cout<<"第"<<index<<"个丑数是"<<uglyNumber(index);  
    
    system("pause");
    return 0;
    }