0166. Fraction to Recurring Decimal

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

Description

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.

If multiple answers are possible, return any of them.

It is guaranteed that the length of the answer string is less than 104 for all the given inputs.

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)"

Example 4:

**Input:** numerator = 4, denominator = 333
**Output:** "0.(012)"

Example 5:

**Input:** numerator = 1, denominator = 5
**Output:** "0.2"

Constraints:

• -231 <= numerator, denominator <= 231 - 1

• denominator != 0

ac

So tedious handling those stackoverflow edge cases.

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

        StringBuilder sb = new StringBuilder();
        Map<Long, Integer> map = new HashMap<Long, Integer>();

        // > 0
        boolean positive = numerator >= 0 && denominator >= 0 || numerator < 0 && denominator < 0;
        long num = Math.abs((long)numerator);
        long den = Math.abs((long)denominator);
        long first = num / den;

        // decimal
        long n = num % den;
        int digits = 0;
        int repeatDigit = -1;
        while (n != 0) {
            if (map.containsKey(n)) {
                repeatDigit = map.get(n);
                break;
            } 
            map.put(n, digits);
            sb.append("" + n * 10 / den);
            n = n * 10 % den;
            digits++;
        }

        String decimal = sb.toString();


        // output
        String res = "";
        if (repeatDigit >= 0) {
            res =  String.format("%d.%s(%s)", first, decimal.substring(0, repeatDigit), decimal.substring(repeatDigit));
        } else if (decimal.length() > 0) {
            res =  "" + first + "." + decimal;
        } else {
            res =  "" + first;
        }

        return positive ? res : "-" + res;

    }
}

/**
before dot: n / d
decimal: n = n % d * 10, keep doing
when repeat (hashmap record position), stop, the part repeats: map.get(i) - last one, enclose with parentheses.
**/