判断循环小数（Java实现）

//输入格式

//a,b

//a、b为整数

import java.io.IOException;import java.util.ArrayList;import java.util.Scanner;public class Main {/** * @param args * @throws IOException  */public static void main(String[] args)  {// TODO Auto-generated method stubScanner sc = new Scanner(System.in);String input = sc.next();String[] inputArr = input.split(",");int numerator = Integer.valueOf(inputArr[0]);int denominator = Integer.valueOf(inputArr[1]);double quotient = (double)numerator/(double)denominator;//如果是循环小数if(isRepeating(numerator, denominator)){//纯循环小数,eg:1/3,1/7if(isPureRepeating(numerator, denominator)){ArrayList<Integer> remainderStack = new ArrayList<Integer>();ArrayList<Integer> quotientStack = new ArrayList<Integer>();int index=0;remainderStack.add((numerator*10)%denominator);quotientStack.add((numerator*10)/denominator);while(true){int back = remainderStack.get(index)*10;while(back<numerator){back=back*10;//remainderStack.add(0);quotientStack.add(0);}if(remainderStack.indexOf(back%denominator)!=-1){//quotientStack.add(back/denominator);//remainderStack.add(back%denominator);int back1 = remainderStack.get(index)*10;while(back1<numerator){back1=back1*10;//remainderStack.add(0);quotientStack.add(0);}index=quotientStack.indexOf(back1/denominator);break;}else {quotientStack.add(back/denominator);remainderStack.add(back%denominator);}index++;}System.out.print(remainderStack);System.out.print(quotientStack);System.out.println(quotientStack.get(index));System.out.print("0.");for(int i = 0;i<index;i++)System.out.print(quotientStack.get(i));System.out.print("[");for(int i = index;i<quotientStack.size();i++)System.out.print(quotientStack.get(i));System.out.print("]");}//混合循环小数,1/6,34/45else{ArrayList<Integer> remainderStack = new ArrayList<Integer>();ArrayList<Integer> quotientStack = new ArrayList<Integer>();int tenNum = numerator*10;int index = 0;int rindex = 0 ;while(tenNum<denominator){remainderStack.add(0);quotientStack.add(0);index++;tenNum*=10;}remainderStack.add(tenNum%denominator);quotientStack.add(tenNum/denominator);while(true){int tenR = remainderStack.get(index)*10;while(tenR<denominator){remainderStack.add(0);quotientStack.add(0);index++;tenR*=10;}if(remainderStack.indexOf(tenR%denominator)!=-1){index = remainderStack.indexOf(tenR%denominator);//特殊处理1/6的情况if(index==0){remainderStack.add(tenR%denominator);quotientStack.add(tenR/denominator);index=remainderStack.lastIndexOf(tenR%denominator);}break;}else{remainderStack.add(tenR%denominator);quotientStack.add(tenR/denominator);index++;//rindex++;}}System.out.print("0.");for(int i = 0;i<index;i++)System.out.print(quotientStack.get(i));System.out.print("[");for(int i = index;i<quotientStack.size();i++)System.out.print(quotientStack.get(i));System.out.print("]");}}//如果不是循环小数else{System.out.print(quotient);}}//判断numerator/denominatoe是否是循环小数public static Boolean isRepeating(int numerator,int denominator){int simpleNum = 0;int simpleDen = 0;if(numerator<denominator){for(int i = numerator;i>0;i--){if(numerator%i==0&&denominator%i==0){simpleNum = numerator/i;simpleDen = denominator/i;break;}}}else{for(int i = denominator;i>0;i--){if(numerator%i==0&&denominator%i==0){simpleNum = numerator/i;simpleDen = denominator/i;break;}}}//如果分数化简后分母除了2,5之外还有素因数，就是无限循环小数for(int i = 2;i<=simpleDen;i++){if(simpleDen%i==0){if(isPrime(i)){if(i!=2&&i!=5)return true;}}}return false;}//判断是否是素数public static boolean isPrime(int n){if(n==1||n==2||n==3)return true;for(int i =2 ;i<n;i++){if(n%i==0)return false;}return true;}//判断是否是纯循环小数，其中numerator<denominatorpublic static boolean isPureRepeating(int numerator,int denominator){int simpleNum = 0;int simpleDen = 0;if(numerator<denominator){for(int i = numerator;i>0;i--){if(numerator%i==0&&denominator%i==0){simpleNum = numerator/i;simpleDen = denominator/i;break;}}}else{for(int i = denominator;i>0;i--){if(numerator%i==0&&denominator%i==0){simpleNum = numerator/i;simpleDen = denominator/i;break;}}}//如果化简后的分母能分解成两个或两个以上素数的乘积，则是混合无限循环小数if(isResolveToTwoPrime(simpleDen))return false;else return true;}//判断分母是否能分解成两个以上素数的乘积，如果是返回false，否则truepublic static  boolean isResolveToTwoPrime(int num)    {        int i;        int count = 0;        for (i = 2; i < num; i++)        {                 while (i != num)            {                if (num % i == 0)                {                count++;                    num /= i;                }                else                    break;            }        }        if(count>=1)return true;        else return false;    }}