title: Painting Fence Algorithm
signature: function paintingFenceAlgorithm($n, $k) {
test_code: <?php
  
  
  // SOLUTION CODE 
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  function validateSolution($actual, $expected){
      return serialize($actual) == serialize($expected);
  }
  
  function driver($n, $k, $expected){
      try{
        if (validateSolution(PLACEHOLDER_FN_NAME($n, $k), $expected)){
          return "PASSED";
        }
        return "FAILED";
      }
      catch (Exception $exception_obj) {
        return get_class($exception_obj);
      }
  }
  
  function main(){
      printf("TEST-0...%s\n",driver(
        6, 30, 
        725841870));
      
      printf("TEST-1...%s\n",driver(
        23, 87, 
        370622679));
      
      printf("TEST-2...%s\n",driver(
        89, 31, 
        7554776));
      
      printf("TEST-3...%s\n",driver(
        63, 36, 
        76740139));
      
      printf("TEST-4...%s\n",driver(
        23, 68, 
        647498520));
      
      printf("TEST-5...%s\n",driver(
        44, 66, 
        70208793));
      
      printf("TEST-6...%s\n",driver(
        81, 18, 
        227130467));
      
      printf("TEST-7...%s\n",driver(
        43, 73, 
        204618786));
      
      printf("TEST-8...%s\n",driver(
        9, 42, 
        797370673));
      
      printf("TEST-9...%s\n",driver(
        41, 98, 
        903959704));
      
  }
  
  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;
  }