LeetCode 166. 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.