[LeetCode]166. Fraction to Recurring Decimal

最新推荐文章于 2019-05-28 15:09:00 发布

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本文介绍了一种将任意两个整数表示的分数转换为循环小数字符串的方法，并通过使用哈希映射记录余数和答案长度来检测循环部分。

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Problem Description

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)”.
[https://leetcode.com/problems/fraction-to-recurring-decimal/]

思路

用Map保存每次除剩下的余数和ans的长度，这样如果出现相同的余数，说明到了循环的起点。。

Code

package q166;

import java.util.HashMap;
import java.util.Map;


public class Solution {

    public String fractionToDecimal(int numerator, int denominator) {
        String ans = "";
        int symbol = 1;
        long mydenominator=(long)denominator;
        long mynumerator=(long)numerator;
        if (mynumerator < 0) {
            symbol *= -1;
            mynumerator *= -1;
        }
        if (mydenominator < 0) {
            symbol *= -1;
            mydenominator *= -1;
        }
        if (symbol < 0&&mynumerator>0)
            ans += "-";
        if (mynumerator / mydenominator > 0)
            ans += mynumerator / mydenominator + "";
        else if(mynumerator / mydenominator==0) ans += "0";


        if (mynumerator % mydenominator == 0)
            return ans;
        else {
            ans += ".";
            int i = 0;
            long a = mynumerator;
            Map<Long,Integer> m=new HashMap<Long,Integer>();
            a -= (Math.ceil(a / mydenominator)) * mydenominator;
            m.put(a, ans.length());
            while (i++ < 3000&&a!=0) {
                a *= 10;
                if(a / mydenominator<0) ans += -a / mydenominator;
                else ans += a / mydenominator;
                a -= (Math.ceil(a / mydenominator)) * mydenominator;
                if(m.containsKey(a)){
                    ans=ans.substring(0,m.get(a))+"("+ans.substring(m.get(a))+")";
                    break;
                }else{
                    m.put(a, ans.length());
                }
            }
        }
        return ans;

    }

//
//  public static void main(String[] args) {
//      Solution s = new Solution();
//      System.out.println(s.fractionToDecimal(-2147483648,-1));
//  }

}