LeetCode 166. Fraction to Recurring Decimal（循环小数）

原题网址：https://leetcode.com/problems/fraction-to-recurring-decimal/

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.

方法：使用哈希映射记录余数和位置。

public class Solution {
public String fractionToDecimal(int numerator, int denominator) {
StringBuilder sb = new StringBuilder();
if ((numerator < 0 && denominator > 0) || (numerator > 0 && denominator < 0)) sb.append("-");
long quotient = (long)numerator / denominator;
sb.append(Math.abs(quotient));
long remainder = (long)numerator % denominator * 10;
if (remainder != 0) {
sb.append(".");
StringBuilder fraction = new StringBuilder();
Map<Long, Integer> nums = new HashMap<>();
// nums.add(numerator);
int pos = 0;
nums.put(remainder, pos++);
do {
int q = (int)Math.abs(remainder / denominator);
fraction.append(q);
remainder = remainder % denominator * 10;
if (nums.containsKey(remainder)) break;
nums.put(remainder, pos++);
} while (remainder != 0);
if (remainder != 0) {
fraction.insert(nums.get(remainder), "(");
fraction.append(")");
sb.append(fraction.toString());
} else {
sb.append(fraction.toString());
}
}
return sb.toString();
}
}