[LeetCode] 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)".

  
  

  这题实现起来还是比较麻烦的，主要还要考虑负数的输入情况，特别是-2147483648这样的整数型的边界值。最简单的方法就是先把所有的输入全部转换为长整型的正数。

  另外，由于要记录小数里循环的部分，所以还需要用到一个Map去记录小数点的每位和对应的余数值。如果碰到的同样的余数值，那么说明遇到了开始循环的部分了。

  	public String fractionToDecimal(int numerator, int denominator) {
  		long longNumerator = Math.abs((long) numerator);
  		long longDenominator = Math.abs((long) denominator);
  
  		StringBuilder sb = new StringBuilder();
  		if ((long) numerator * denominator < 0) sb.append("-");
  		sb.append(longNumerator / longDenominator);
  
  		long remainder = longNumerator % longDenominator;
  		if (remainder == 0) return sb.toString();
  		sb.append(".");
  
  		StringBuilder fracSb = new StringBuilder();
  		Map
      
        map = new HashMap
       
        (); int index = 0; while (remainder != 0) { remainder *= 10; long nextRemainder = remainder % longDenominator; // If repeated part occurs. if (map.containsKey(remainder)) { fracSb.insert(map.get(remainder), "("); fracSb.append(")"); break; } map.put(remainder, index++); fracSb.append(remainder / longDenominator); remainder = nextRemainder; } sb.append(fracSb); return sb.toString(); }