title: Double Factorial
signature: function doubleFactorial(n: number): number {
test_code: 
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  function convertToString(value: any): string{
      return JSON.stringify(value, function (key, val) {
          if (val instanceof Set) {
              return Array.from(val);
          } return val;});
  }
  
  function validateSolution(actual: number, expected: number): boolean {
      return convertToString(actual) === convertToString(expected);
  }
  
  function driver(n: number, expected:number): string {
      try{
          if (validateSolution(PLACEHOLDER_FN_NAME(n),expected)){
              return "PASSED";
          }
          return "FAILED";
      } catch (error) {
        return error.name;
      }
      
  }
      
  function main(){
    let result = '';
    result = driver(15, 2027025);
    console.log(`TEST-0...${result}`);
  
    result = driver(21, 13749310575);
    console.log(`TEST-1...${result}`);
  
  };
  
  main();
source_py: def double_factorial(n):
      if ((n == 0) or (n == 1)):
          return 1
      return (n * double_factorial((n - 2)))
source_cpp: unsigned int double_factorial(unsigned int n) {
    if ( n == 0 || n == 1 ) return 1;
    return n * double_factorial ( n - 2 );
  }