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## Problem

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)"


## Code

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

StringBuilder res = new StringBuilder();
String sign = (numerator > 0) ^ (denominator > 0) ? "-" : "";
res.append(sign);

long num = Math.abs((long)numerator);
long den = Math.abs((long)denominator);

res.append(num / den);
num %= den;

if (num == 0) {
return res.toString();
}

res.append(".");

HashMap<Long, Integer> map = new HashMap<Long, Integer>();
map.put(num, res.length());

while (num != 0) {
// 除法过程
num *= 10;
res.append(num / den);
num %= den;
if (map.containsKey(num)) {
int index = map.get(num);
res.insert(index, "(");
res.append(")");
break;
} else {
map.put(num, res.length());
}
}
return res.toString();
}
}