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面试题-判断无限循环小数
source link: https://rhetty.github.io/2019/08/06/%E9%9D%A2%E8%AF%95%E9%A2%98-%E5%88%A4%E6%96%AD%E6%97%A0%E9%99%90%E5%BE%AA%E7%8E%AF%E5%B0%8F%E6%95%B0/
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面试题-判断无限循环小数
发表于 2019-08-06
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题目：正整数A、B，判断A/B是否为无限循环小数，若是，找出循环部分。如1/7，循环部分为142857。
* 判断两数相除是否为无限循环小数，如果是，找出循环的部分
public class RepeatDecimal
private int _dividend;
private int _divider;
public RepeatDecimal(int dividend, int divider)
_dividend = dividend;
_divider = divider;
* 判断是否为无限循环小数
public bool IsRpeatDecimal()
// 分子为0
if (_dividend == 0) return false;
// 分母为0
if (_divider == 0) throw new Exception("Divider is zero");
// 先找到最大公约数，化为最简分数
var gcd = getGCD();
int tmp = _divider / gcd;
// 分母存在2、5以外的因数，则无限循环
while (tmp % 2 == 0) tmp /= 2;
while (tmp % 5 == 0) tmp /= 5;
return tmp != 1;
* 获取循环部分
public string GetRepeatPart()
if (!IsRpeatDecimal()) return null;
string result = "";
var a = Math.Abs(_dividend);
var b = Math.Abs(_divider);
// 模拟除法
List<int> decimals = new List<int>();
while (a > b) a -= b;
while (true)
while (a < b) {
a *= 10;
// 如果商之前得到过，则找到了循环部分
int quotient = a / b;
int index = decimals.IndexOf(quotient);
if (index >= 0)
for (var i = index; i < decimals.Count; ++i)
result += decimals[i];
break;
decimals.Add(quotient);
a %= b;
return result;
private int getGCD()
int a = _dividend;
int b = _divider;
int c = 0;
while (true)
c = a % b;
if (b == 0)
return a;
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