LeetCode Fraction to Recurring Decimal

原题链接在这里：https://leetcode.com/problems/fraction-to-recurring-decimal/

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.

Example 1:

Input: numerator = 1, denominator = 2
Output: "0.5"

Example 2:

Input: numerator = 2, denominator = 1
Output: "2"

Example 3:

Input: numerator = 2, denominator = 3
Output: "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:

 public class Solution {
     public String fractionToDecimal(int numerator, int denominator) {
         if(numerator == 0){
             return "0";
         }
         if(denominator == 0){
             return "";
         }

         StringBuilder res = new StringBuilder();
         long num = Math.abs((long)numerator);
         long deno = Math.abs((long)denominator);

         //如果是负数
         if((numerator < 0) ^ (denominator < 0)){
             res.append("-");
         }

         res.append(num/deno);
         long reminder = num%deno;
         if(reminder == 0){
             return res.toString();
         }

         //有小数
         res.append(".");
         //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
         HashMap<Long, Integer> hm = new HashMap<Long, Integer>();
         StringBuilder desRes = new StringBuilder();
         while(reminder != 0){
             if(hm.containsKey(reminder)){ //出现了循环，找到循环开始的index添加左括号
                 int beginIndex = hm.get(reminder);
                 desRes.insert(beginIndex, "(");
                 desRes.append(")");
                 res.append(desRes);
                 return res.toString();
             }
             hm.put(reminder, desRes.length());
             desRes.append(reminder*10/deno);
             reminder = (reminder*10)%deno;
         }
         res.append(desRes);
         return res.toString();
     }
 }

与Decimal To Fraction 小数转换成分数类似.