166. Fraction to Recurring Decimal

题目：

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)".

链接： http://leetcode.com/problems/fraction-to-recurring-decimal/

题解：

这道题基本就是Divide Two Integers + 处理循环小数。一刷的时候果断放弃了，因为不想处理恶心的边界条件，不在一开始把int转为long的话后面会很难写。现在又看了一遍大家的答案，发现绝大多数是先把int转为long，我也就放心了。实在不行咱可以用Python写这个。

Java:

Time Complexity - O(n)， Space Complexity - O(n)

public class Solution {

    public String fractionToDecimal(int numerator, int denominator) {

        if (numerator == 0) return "0";

        if (denominator == 0) throw new ArithmeticException();

        boolean sameSign = (numerator > 0) ^ (denominator < 0);

        long dividend = Math.abs((long)numerator);

        long divisor = Math.abs((long)denominator);

        String intPart = String.valueOf(dividend / divisor);

        intPart = sameSign ? intPart : "-" + intPart;

        long remainder = dividend % divisor;

        if (remainder == 0) return intPart;

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

        StringBuilder decimalPart = new StringBuilder();     

        while (remainder != 0) {

            map.put(remainder, decimalPart.length());

            remainder *= 10;

            decimalPart.append(remainder / divisor);

            remainder = remainder % divisor;

            if (map.containsKey(remainder)) {

                decimalPart.insert(map.get(remainder), "(");

                decimalPart.append(')');

                break;

            }

        }

        return intPart + "." + decimalPart.toString();

    }

}

二刷:

一样的方法，一样的code，写起来还是很吃力，多多练习吧。

Java:

public class Solution {

    public String fractionToDecimal(int numerator, int denominator) {

        if (numerator == 0) return "0";

        if (denominator == 0) throw new ArithmeticException("Divide by zero");

        boolean sameSign = (numerator > 0) ^ (denominator < 0);

        long dividend  = Math.abs((long)numerator);

        long divisor  = Math.abs((long)denominator);

        StringBuilder sb = new StringBuilder();

        if (!sameSign) sb.append("-");

        sb.append(dividend / divisor);

        dividend %= divisor;

        if (dividend == 0) return sb.toString();

        sb.append(".");

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

        while (dividend != 0) {

            map.put(dividend, sb.length());

            dividend *= 10;

            sb.append(dividend / divisor);

            dividend %= divisor;

            if (map.containsKey(dividend)) {

                sb.insert(map.get(dividend), "(");

                sb.append(")");

                return sb.toString();

            }

        }

        return sb.toString();

    }

}

Test Cases:

(1, 3)
(1, 5)
(1, 6)
(1, 90)
(1, 99)
(22, 7)
(-50, 8)
(0, -5)
(-1, -2147483648)
(-2147483648, 1)

Reference：

https://leetcode.com/discuss/18731/accepted-cpp-solution-with-explainations

https://leetcode.com/discuss/18769/there-good-deal-with-extreme-edge-case-without-converting-long

https://leetcode.com/discuss/18989/online-judge-pass-java-version

https://leetcode.com/discuss/20515/my-java-solution

https://leetcode.com/discuss/22652/do-not-use-python-as-cpp-heres-a-short-version-python-code

https://leetcode.com/discuss/23079/my-clean-java-solution

https://leetcode.com/discuss/31521/short-java-solution

https://leetcode.com/discuss/42159/0ms-c-solution-with-detailed-explanations

https://leetcode.com/discuss/50512/accepted-clean-java-solution

http://gqqnbig.me/?p=160

http://blog.csdn.net/hanshileiai/article/details/8861376

http://segmentfault.com/q/1010000003958185

https://leetcode.com/discuss/8886/my-simple-solution

http://blog.csdn.net/ljiabin/article/details/42025037

巴特西

166. Fraction to Recurring Decimal

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