iOS中排列组合算法的使用小结

解决的思路就是为了不让数字值越界，可以让分子和分母约分后，再乘下一个分子，再和分母约分。以此类推。话不多说，直接上代码：

/**
 双色球 普通选注
 */
- (long)lotterySSQPTRecursiveWithRedBalls:(NSUInteger)redBalls blueBalls:(NSUInteger)blueBalls{
 if (redBalls > 5 && blueBalls > 0) {
 if (redBalls == 6) {
  return blueBalls;
 }else{
  NSUInteger count = (redBalls-6 > 6) ? 6 : redBalls-6;
  long number = 1;
  long molecular = 1;
  long denominator = 1;
  for (int i = 0; i < count; i++) {
  molecular = molecular*(redBalls-i);
  denominator = denominator * (i+1);
  number = (molecular*number)/denominator;
  molecular = 1;
  denominator = 1;
  }
  number = number*blueBalls;
  
  return number;
 }
 }else{
 return 0;
 }
}