166. Fraction to Recurring Decimal

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本文介绍了一种将任意两个整数表示的分数转换为字符串格式的方法，特别关注如何识别和表示循环小数部分。通过使用基本数学知识和长除法概念，提供了一个具体的Java实现方案。

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)".

Hint:

No scary math, just apply elementary math knowledge. Still remember how to perform a long division?
Try a long division on 4/9, the repeating part is obvious. Now try 4/333. Do you see a pattern?
Be wary of edge cases! List out as many test cases as you can think of and test your code thoroughly.

Code:

public class Solution {
    public String fractionToDecimal(int numerator, int denominator) {
        return getInt(numerator,denominator) + getDec(numerator,denominator);
        
    }
    
    String getInt(int num, int denum){
        String sign = ((num > 0) == (denum > 0) || num == 0) ? "" : "-";
        long n = Math.abs((long) num);
        long dn = Math.abs((long) denum);
        return sign + (n/dn);
    }
    
    String getDec(int num, int denum){
        long n = Math.abs((long) num);
        long dn = Math.abs((long) denum);
        n = n % dn;
        if(n == 0) return "";
        HashMap<Long,Integer> hm = new HashMap<>();
        StringBuilder sb = new StringBuilder();
        sb.append(".");
        while(n != 0 && !hm.containsKey(n)){
            long t = (n * 10) / dn;
            hm.put(n,sb.length());
            sb.append(t);
            n = (n * 10) % dn;
            
        }
        if(n != 0){
            sb.insert(hm.get(n),"(");
            sb.append(")");
        }
        return sb.toString();
    }
}