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)".

[分析]

关键是确定发生循环的位置, 使用map存所有余数, 当余数已经出现过时, 即发生了循环.

[注意]

Overflow, 符号的处理, 分开两个函数, 使代码更容易读

[CODE]

public class Solution {
    public String fractionToDecimal(int numerator, int denominator) {
        
        long num = numerator;
        long den = denominator;
        boolean neg = num * den < 0;
        num = Math.abs(num);
        den = Math.abs(den);

        String res = neg ? "-" + Long.toString(num/den) : Long.toString(num/den);
        long remainder = num%den;
        
        return (remainder==0) ? res : (res + "." + getDec(remainder, den));        
    }
    
    private StringBuilder getDec(long remainder, long den) {
        Map<Long, Integer> map = new HashMap<Long, Integer>();
        int i=0;
        StringBuilder sb = new StringBuilder();
        while(remainder!=0 && !map.containsKey(remainder)) {
        	map.put(remainder, i);
        	++i;
        	remainder *= 10;
        	sb.append(Long.toString(remainder/den));
        	remainder %= den;
        }
        
        if(remainder!=0){
            sb.insert((int)map.get(remainder), '(');
            sb.append(')');
        }
        return sb;
    }
}

leetcode 166: Fraction to Recurring Decimal