Binary Representation

Given a (decimal - e.g. 3.72) number that is passed in as a string, return the binary representation that is passed in as a string. If the fractional part of the number can not be represented accurately in binary with at most 32 characters, return ERROR.

Example

For n = "3.72", return "ERROR".

For n = "3.5", return "11.1".

分析：

分成两个部分，整数部分用%和/，小数部分 *2 如果 <1 就为0，基数=基数；大于1,就为1,基数=基数-1 

比如：
0.6*2=1.2>0 那么就为1 基数=1.2-1=0.2

0.2*2=0.4<0 那么就为0,基数=0.4

0.4*2=0.8<0,那么就为0,基数=0.8

0.8*2=1.6>0 那么就为1,基数为1.6-1=0.6
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所以5.6可以表示为:101.1001

public class Solution {
    /**
     *@param n: Given a decimal number that is passed in as a string
     *@return: A string
     */
    public String binaryRepresentation(String n) {
        int intPart = Integer.parseInt(n.substring(0, n.indexOf('.')));
        double decPart = Double.parseDouble(n.substring(n.indexOf('.')));
        String intstr = "";
        String decstr = "";
        
        if (intPart == 0) intstr += '0';
        while (intPart > 0) {
            int c = intPart % 2;
            intstr = c + intstr;
            intPart = intPart / 2;
        }
       int count = 0;
        while (decPart > 0.0 && count <= 32) {
            double r = decPart * 2;
            if (r >= 1.0) {
                decstr += '1';
                decPart = r - 1.0;
            }else {
                decstr += '0';
                decPart = r;
            }
            count++;
        }
        
        if (count > 32) return "ERROR";
        return decstr.length() > 0? intstr + "." + decstr : intstr;
    }
}