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(); }