LeetCode 166. Fraction to Recurring Decimal

i_chase

于 2019-05-31 18:32:22 发布

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本文链接：https://blog.youkuaiyun.com/qq_39638957/article/details/90721231

博客提出将分数的分子和分母两个整数转换为字符串格式的问题，若小数部分有循环，需将循环部分用括号括起来，并给出了示例。

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 {
    
    //一旦出现了重复的余数，就说明结果是无限循环小数
    public String fractionToDecimal(int numerator, int denominator) {
        
        if(numerator == 0) {
            return "0";
        }
        
        StringBuilder res = new StringBuilder();
        //numerator和denominator都不为0
        res.append( (numerator > 0) ^ (denominator > 0) ? "-" : "" );//符号位
        
        long num = Math.abs((long)numerator);
        long den = Math.abs((long)denominator);
        
        //integral part
        res.append(num / den);//商
        num %= den;//余数
        if(num == 0){//整除了
            return res.toString();
        }
        
        // fractional part
        res.append(".");
        HashMap<Long, Integer> map = new HashMap<Long, Integer>();
        map.put(num, res.length());//记录余数 以及 (余数*10)除以denominator的商位置
        
        while (num != 0) {
            num *= 10;
            res.append(num / den);
            num %= den;
            if(map.containsKey(num)) {//余数出现重复
                int index = map.get(num);
                res.insert(index, "(");
                res.append(")");
                break;
            }
            else{
                map.put(num, res.length());
            }
        }
        return res.toString();//string builder to string
    }
    
}