leetCode 166. Fraction to Recurring Decimal

1.题目

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.

If the fractional part is repeating, enclose the repeating part in parentheses.

For example,

Given numerator = 1, denominator = 2, return “0.5”.
Given numerator = 2, denominator = 1, return “2”.
Given numerator = 2, denominator = 3, return “0.(6)”.

题目的基本意思是给出分子和分母，求出表示的数。如果是无限循环小数，用括号把循环体括起来

2.算法

这题的思路是依次除以除数，并对除数取余，然后得到下一位，如果余数为0，说明不是无限循环小数，如果有两个余数相同，就是循环小数，然后找出循环的位置，加上括号

public class Solution {    public String fractionToDecimal(int numerator, int denominator) {        if (numerator == 0) return new String("0");        boolean flag = (numerator < 0)^(denominator < 0);        long Numerator = Math.abs((long)numerator);        long Denominator = Math.abs((long)denominator);        StringBuffer res = new StringBuffer();        if (flag == true) res.append('-');        res.append(String.valueOf((Numerator / Denominator)));        Numerator = Numerator % Denominator;        if (Numerator == 0) return res.toString();        res.append('.');        HashMap<Long, Integer> map = new HashMap<Long, Integer>();        for (int i = res.length(); Numerator != 0; ++i) {            if (map.get(Numerator) != null) break;            map.put(Numerator, i);            Numerator *= 10;            res.append(String.valueOf((Numerator / Denominator)));            Numerator %= Denominator;        }                if (Numerator == 0) return res.toString();        res.insert(map.get(Numerator),"(");        res.append(')');        return res.toString();}