丑数(空间换时间)

获取第N个丑数的C++实现

最新推荐文章于 2020-02-04 12:07:34 发布

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本文介绍了一种使用C++编程语言来寻找第N个丑数的方法。丑数是指只包含质因数2、3和5的正整数。通过动态规划的方式，该算法能够有效地找到指定位置的丑数，并且详细展示了如何维护和更新候选丑数的序列。

#include <iostream>
#include <stdlib.h>
using namespace std;

int Getuglynumber(int index);
int Min(int number1,int number2,int number3);

int main(){
	int index;
	cin>>index;
	int result = Getuglynumber(index);
	cout<<result<<endl;
	return 0;
}

int Min(int number1,int number2,int number3){
	int min = (number1<number2)?number1:number2;
	min = (min<number3)?min:number3;
	return min;
}

int Getuglynumber(int index){
	if(index<=0) return 0;
	
	int *puglynumbers = new int[index];
	puglynumbers[0] = 1;
	int nextuglyindex =  1;
	
	int *pmultiply2 = puglynumbers;
	int *pmultiply3 = puglynumbers;
	int *pmultiply5 = puglynumbers;
	
	while(nextuglyindex < index){
		int min = Min(*pmultiply2*2,*pmultiply3*3,*pmultiply5*5);
		
		puglynumbers[nextuglyindex] = min;
		
		while(*pmultiply2*2<=puglynumbers[nextuglyindex])
		++pmultiply2;
		while(*pmultiply3*3<=puglynumbers[nextuglyindex])
		++pmultiply3;
		while(*pmultiply5*5<=puglynumbers[nextuglyindex])
		++pmultiply5;
		
		++nextuglyindex;
	}
	
	int ugly = puglynumbers[nextuglyindex-1];
	delete[] puglynumbers;
	return ugly;
}