title: Painting Fence Algorithm
signature: function painting_fence_algorithm(n, k)
test_code: using Printf
  
  # SOLUTION CODE
  # ============================================
  PLACEHOLDER_CODE_BODY
  
  # TESTING CODE 
  # ============================================
  function validate_solution(actual, expected)
      return actual == expected
  end
  
  function driver(n, k, expected)
      try
  
          if validate_solution(PLACEHOLDER_FN_NAME(n, k), expected)
              return "PASSED";
          end
          return "FAILED";
      catch exception_obj
          return string(Base.typename(typeof(exception_obj)).wrapper);
      end
  end
  
  function main()
      
      result = driver(6, 30, 725841870);
      @printf("TEST-0...%s\n",result);
      
      result = driver(23, 87, 370622679);
      @printf("TEST-1...%s\n",result);
      
      result = driver(89, 31, 7554776);
      @printf("TEST-2...%s\n",result);
      
      result = driver(63, 36, 76740139);
      @printf("TEST-3...%s\n",result);
      
      result = driver(23, 68, 647498520);
      @printf("TEST-4...%s\n",result);
      
      result = driver(44, 66, 70208793);
      @printf("TEST-5...%s\n",result);
      
      result = driver(81, 18, 227130467);
      @printf("TEST-6...%s\n",result);
      
      result = driver(43, 73, 204618786);
      @printf("TEST-7...%s\n",result);
      
      result = driver(9, 42, 797370673);
      @printf("TEST-8...%s\n",result);
      
      result = driver(41, 98, 903959704);
      @printf("TEST-9...%s\n",result);
      
  end
  
  main()
source_py: def painting_fence_algorithm(n, k):
      total = k
      mod = 1000000007
      (same, diff) = (0, k)
      for i in range(2, (n + 1)):
          same = diff
          diff = (total * (k - 1))
          diff = (diff % mod)
          total = ((same + diff) % mod)
      return total
source_cpp: long painting_fence_algorithm(int n, int k) {
    long total = k;
    int mod = 1000000007;
    int same = 0, diff = k;
    for ( int i = 2;
    i <= n;
    i ++ ) {
      same = diff;
      diff = total * ( k - 1 );
      diff = diff % mod;
      total = ( same + diff ) % mod;
    }
    return total;
  }