水仙花数优化问题:穷举法、查找表法、组合数学法

package yxj.Test;


import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Arrays;


public class ShuiXianHua {
static long searchTable[]=new long [10];
static String s=null;


/**
* @param args
*/
public static void main(String[] args) {
int length_=8;
long biStart_ = 10000000;
long biEnd_ = 99999999;

//穷举法
//Jisuan1(biStart_,biEnd_,length_);

//查找表法
initSearchTable(length_);
Jisuan2(biStart_,biEnd_,length_);

//组合数学
//int [] tint={1,6,3,4};
//isSXHS(tint);
smartRetrospectiveSearch(length_);
}

public static void smartRetrospectiveSearch(int n)
{
//组合数学
long start=System.currentTimeMillis();
System.out.println("组合数学:");
int [] num= new int[n];
int i=0;
while(true)
{
if(i==n-1)
{
isSXHS(num);
}
else
{
i++;
num[i]=num[i-1];
continue;
}
while(i>=0&&num[i]==9)
{
i--;
}
if(i>=0)
{
num[i]++;
}
else
{
break;
}
}
long end=System.currentTimeMillis();
System.out.println("Time:"+(end-start)+"ms");
}

public static void isSXHS(int[] num)
{
BigInteger bit=BigInteger.valueOf(0);
for(int a:num)
{
bit=bit.add(BigInteger.valueOf(searchTable[a]));
}
int[] tnum=new int [num.length];
s=bit.toString();
if(s.length()>num.length)
{
return;
}
for(int i=0;i<s.length();i++)
{
tnum[i]=s.charAt(i)-'0';
}
Arrays.sort(tnum);
if(Arrays.equals(num, tnum)&&s.length()==num.length)
{
System.out.println(bit);
}
}

public static void Jisuan1(long biStart_,long biEnd_,int length_)
{
System.out.println("穷举法：");
long start=System.currentTimeMillis();
long biStart = biStart_;
long biEnd = biEnd_;
int length=length_;
outer:for(long bi=biStart;bi<=biEnd;bi++)
{
int biTest=0;
s=bi+"";
for(int i=0;i<length;i++)
{
biTest=biTest+(int)Math.pow((s.charAt(i)-'0'), length);
if(biTest>bi)
{
continue outer;
}
}
if(bi==biTest)
{
System.out.println(bi);
}
}
long end=System.currentTimeMillis();
System.out.println("Time:"+(end-start)+"ms");
}


public static void initSearchTable(int length)
{
for(int i=0;i<10;i++)
{
searchTable[i]=(long)Math.pow(i, length);
}
}

public static void Jisuan2(long biStart_,long biEnd_,int length_)
{
System.out.println("查找表法：");
long start=System.currentTimeMillis();
long biStart = biStart_;
long biEnd = biEnd_;
int length=length_;
outer:for(long bi=biStart;bi<=biEnd;bi++)
{
long biTest=0;
s=bi+"";
for(int i=0;i<length;i++)
{
biTest=biTest+searchTable[s.charAt(i)-'0'];
if(biTest>bi)
{
continue outer;
}
}
if(bi==biTest)
{
System.out.println(bi);
}
}
long end=System.currentTimeMillis();
System.out.println("Time:"+(end-start)+"ms");
}

}

结果：

查找表法：
24678050
24678051
88593477
Time:41078ms
组合数学:
24678050
24678051
88593477
Time:62ms