- #1

SlurrerOfSpeech

- 141

- 11

Code:

```
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution
{
// Returns the number represented by the digits in the array
// within the range of indices [i, j)
static long NumberInRange(long[] arr, long i, long j)
{
long result = 0;
for(; i < j; ++i)
{
result *= 10;
result += arr[i];
}
return result;
}
// Returns true or false depending on whether k is Kaprekar
static bool IsKaprekar(int k)
{
// Must use long to hold square of ints
long square = k * k;
// Get all digits of square in an array of longs
long[] digits = square.ToString().Select(c => (long)Char.GetNumericValue(c)).ToArray();
// Edge case: If there is 1 or fewer digits, return true or false depending on whether
// the square is equal to the original number.
if(digits.Length < 2)
return square == k;
// Get all combinations of array divided into non-empty left and right sides.
// Return early with true if the sum of the left and right equal k.
for(int i = 1; i < digits.Length; ++i)
{
// Get number represented by digits in the range of indices [0,i)
long left = NumberInRange(digits, 0, i);
// Get number represented by digits in the range of indices [i, digits.Length)
long right = NumberInRange(digits, i, digits.Length);
// "By convention, the second part may start with the digit 0, but must be nonzero."
// https://en.wikipedia.org/wiki/Kaprekar_number
if(right == 0)
continue;
// If made it here, we can do the check.
if((right + left) == k)
return true;
}
// If made it here, k is not Kaprekar
return false;
}
static void Main(String[] args)
{
int p = int.Parse(Console.ReadLine());
int q = int.Parse(Console.ReadLine());
IEnumerable<int> kaprekars = Enumerable.Range(p, q - p + 1).Where(k => IsKaprekar(k));
Console.WriteLine(kaprekars.Any() ? string.Join(" ", kaprekars) : "INVALID RANGE");
}
}
```

I am passing most of the test cases but am failing the following 3.

(1)

1000

10000

(2)

1

10000

(3)

1

99999