给定三个整数a，b和c，在小数点后的a / b中查找c的第一个匹配项。如果不存在，则打印-1。
例子：
Input : a = 2 b = 3 c = 6
Output : 1
Explanation:
0.666666.. so 6 occurs at first place
of a/b after decimal point
Input : a = 1 b = 4 c = 5
Output : 2
Explanation:
1 / 4 = 0.25 which gives 5's position
to be 2.一个简单的方法是执行除法并保留小数部分，然后迭代并检查给定的数字是否存在。当完成诸如2/3之类的除法时，这将无法很好地工作，因为它会产生0.666666666，但是在编程语言中，它将把它四舍五入为0.666667，因此我们得到的7在原始a / b中也不存在
一种有效的方法是数学方法，如果我们每次将a乘以b并将其乘以10，我们每次都会得到小数部分后的整数。所需的调制次数为b，因为在小数点后最多有b个整数。因此，我们将其与c进行比较，如果存在，则得到我们想要的值。
下面是上述方法的实现：
C++
// CPP program to find first occurrence
// of c in a/b
#include
using namespace std;
// function to print the first digit
int first(int a, int b, int c)
{
// reduce the number to its mod
a %= b;
// traverse for every decimal places
for (int i = 1; i <= b; i++)
{
// get every fraction places
// when (a*10/b)/c
a = a * 10;
// check if it is equal to
// the required integer
if (a / b == c)
return i;
// mod the number
a %= b;
}
return -1;
}
// driver program to test the above function
int main()
{
int a = 1, b = 4, c = 5;
cout << first(a, b, c);
return 0;
} Java
// Java program to find first occurrence
// of c in a/b
import java.util.*;
import java.lang.*;
public class GfG{
// Function to print the first digit
public static int first(int a, int b, int c)
{
// Reduce the number to its mod
a %= b;
// Traverse for every decimal places
for (int i = 1; i <= b; i++)
{
// Get every fraction places
// when (a*10/b)/c
a = a * 10;
// Check if it is equal to
// the required integer
if (a / b == c)
return i;
// Mod the number
a %= b;
}
return -1;
}
// Driver function
public static void main(String argc[]){
int a = 1, b = 4, c = 5;
System.out.println(first(a, b, c));
}
}
/* This code is contributed by Sagar Shukla */Python3
# Python3 program to find first occurrence
# of c in a/b
# function to print the first digit
def first( a , b , c ):
# reduce the number to its mod
a %= b
# traverse for every decimal places
for i in range(1, b + 1):
# get every fraction places
# when (a*10/b)/c
a = a * 10
# check if it is equal to
# the required integer
if int(a / b) == c:
return i
# mod the number
a %= b
return -1
# driver code to test the above function
a = 1
b = 4
c = 5
print(first(a, b, c))
# This code is contributed by "Sharad_Bhardwaj".C#
// C# program to find first occurrence
// of c in a/b
using System;
public class GfG{
// Function to print the first digit
public static int first(int a, int b, int c)
{
// Reduce the number to its mod
a %= b;
// Traverse for every decimal places
for (int i = 1; i <= b; i++)
{
// Get every fraction places
// when (a*10/b)/c
a = a * 10;
// Check if it is equal to
// the required integer
if (a / b == c)
return i;
// Mod the number
a %= b;
}
return -1;
}
// Driver function
public static void Main() {
int a = 1, b = 4, c = 5;
Console.WriteLine(first(a, b, c));
}
}
/* This code is contributed by vt_m */PHP
Javascript
输出：
2