原题链接在这里：

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)".

题解：

加入整数部分后，在reminder 不为0的时候添加小数部分，用HashMap来维护reminder 和 对应的小数长度. 若是出现无限循环可以找到加左括号的起始点.

AC Java:

1 public class Solution { 2     public String fractionToDecimal(int numerator, int denominator) { 3         if(numerator == 0){ 4             return "0"; 5         } 6         if(denominator == 0){ 7             return ""; 8         } 9         10         StringBuilder res = new StringBuilder();11         long num = Math.abs((long)numerator);12         long deno = Math.abs((long)denominator);13         14         //如果是负数15         if((numerator < 0) ^ (denominator < 0)){16             res.append("-");17         }18         19         res.append(num/deno);20         long reminder = num%deno;21         if(reminder == 0){22             return res.toString();23         }24         25         //有小数26         res.append(".");27         //HashMap中计入reminder 和 对应的小数部分长度，用来找到循环开始的位置28         HashMap
     
       hm = new HashMap
      
       ();29         StringBuilder desRes = new StringBuilder();30         while(reminder != 0){31             if(hm.containsKey(reminder)){ //出现了循环，找到循环开始的index添加左括号32                 int beginIndex = hm.get(reminder);33                 desRes.insert(beginIndex, "(");34                 desRes.append(")");35                 res.append(desRes);36                 return res.toString();37             }38             hm.put(reminder, desRes.length());39             desRes.append(reminder*10/deno);40             reminder = (reminder*10)%deno;41         }42         res.append(desRes);43         return res.toString();44     }45 }
      
     

与类似.