LeetCode: 166. Fraction to Recurring Decimal

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166. Fraction to Recurring Decimal

LeetCode - Fraction to Recurring Decimal

需要注意的是是：在 Map 中放的是被除数，而不是计算出来的位数digit。这样更方便处理！

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)"

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/**
 * Runtime: 1 ms, faster than 100.00% of Java online submissions for Fraction to Recurring Decimal.
 *
 * Memory Usage: 34.8 MB, less than 100.00% of Java online submissions for Fraction to Recurring Decimal.
 *
 * Copy from: https://leetcode.com/problems/fraction-to-recurring-decimal/discuss/51106/My-clean-Java-solution[My clean Java solution - LeetCode Discuss]
 */
public String fractionToDecimal(int numerator, int denominator) {
    if (numerator == 0) {
        return "0";
    }
    StringBuilder result = new StringBuilder();
    result.append(numerator > 0 ^ denominator > 0 ? "-" : "");
    long num = Math.abs((long) numerator);
    long den = Math.abs((long) denominator);
    if (num > den) {
        result.append(num / den);
    } else {
        result.append("0");
    }
    num %= den;
    if (num == 0) {
        return result.toString();
    }
    result.append(".");
    Map<Long, Integer> numToIndexMap = new HashMap<>();
    // 这里需要注意，在 Map 中放的是被除数，而不是计算出来的位数digit。
    numToIndexMap.put(num, result.length());
    while (num != 0) {
        num *= 10;
        result.append(num / den);
        num %= den;
        if (numToIndexMap.containsKey(num)) {
            Integer index = numToIndexMap.get(num);
            result.insert(index, "(");
            result.append(")");
            break;
        } else {
            numToIndexMap.put(num, result.length());
        }
    }

    return result.toString();
}