leetcode学习笔记35

166. 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.

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)”

class Solution {  
    public String fractionToDecimal(int numerator, int denominator) {
    	StringBuffer res=new StringBuffer();
        long num=numerator,deno=denominator;
    	if(numerator==0)
    		return "0";
    	//1.判断符号
    	int sign=1;
    	if(num<0) {
    		sign=-sign;
    		num=Math.abs(num);
    	}
    	if(deno<0){
    		sign=-sign;
    		deno=Math.abs(deno);
    	}
    	if(sign==-1) {
    		res.append("-");
    	}
        //2.算整数部分
        long res_num=num/deno;
        num=num%deno;
        res.append(res_num);
        //3.算小数部分
        if(num!=0){
            res.append(".");
            StringBuffer res_decimal=new StringBuffer();
            HashMap<Long,Integer> hm=new  HashMap<Long,Integer>();
            int index=0;
            while(num!=0){ 
            	num*=10;
                if(hm.containsKey(num)){
                    res_decimal.insert(hm.get(num),"(");
                    res_decimal.append(")");
                    break;
                }
                hm.put(num,index++);
                res_num=num/deno;
                num=num%deno;
                res_decimal.append(res_num);
            }
            res.append(res_decimal);
        }
        return res.toString();     
    }
}