Question

问题如下。 main（）通过调用isPrime（）来检查数字1-10。我认为我的数学是正确的，但是除了2之外的每个数字都不是素数。

我已经检查了一些关于SO的解决方案和问题，但是，我似乎无法达到相同的结果。

原始问题：

public class PrimeChecker {
// Returns 0 if value is not prime, 1 if value is prime
   public static int isPrime(int testVal, int divVal) {
      // Base case 1: 0 and 1 are not prime, testVal is not prime

      // Base case 2: testVal only divisible by 1, testVal is prime

      // Recursive Case
         // Check if testVal can be evenly divided by divVal
         // Hint: use the % operator

         // If not, recursive call to isPrime with testVal and (divVal - 1)
      return 0;
   }

   public static void main(String[] args) {
      int primeCheckVal = 0; // Value checked for prime

      // Check primes for values 1 to 10
      for (primeCheckVal = 1; primeCheckVal <= 10; ++primeCheckVal) {
         if (isPrime(primeCheckVal, (primeCheckVal - 1)) == 1) {
            System.out.println(primeCheckVal + " is prime.");
         }
         else {
            System.out.println(primeCheckVal + " is not prime.");
         }
      }
   }
}

到目前为止我的解决方案：

     public class PrimeChecker {
     // Returns 0 if value is not prime, 1 if value is prime
   public static int isPrime(int testVal, int divVal) {
      int resultVal = 0;

      if ((testVal == 0) || (testVal == 1)){
         resultVal = 0;
      }// Base case 1: 0 and 1 are not prime, testVal is not prime

      else if (divVal == 1) {
         resultVal = 1;
      }// Base case 2: testVal only divisible by 1, testVal is prime

      else {
         if((testVal % divVal != 0) && (testVal / divVal == 1)) {
            isPrime(testVal, (divVal-1));
         }
         else {            
             resultVal = 1;

      }
      }
      return resultVal;
       }

      public static void main(String[] args) {
      int primeCheckVal = 0; // Value checked for prime

      // Check primes for values 1 to 10
      for (primeCheckVal = 1; primeCheckVal <= 10; ++primeCheckVal) {
        if (isPrime(primeCheckVal, (primeCheckVal - 1)) == 1) {
            System.out.println(primeCheckVal + " is prime.");
         }
         else {
            System.out.println(primeCheckVal + " is not prime.");
         }
      }
   }
}

Answer 1

更改if / else块

     if((testVal % divVal != 0) && (testVal / divVal == 1)) {
        isPrime(testVal, (divVal-1));
     }
     else {            
         resultVal = 1;

  }

到

if (testVal % divVal != 0) {
  return isPrime(testVal, (divVal-1));
} else {            
  resultVal = 0;
}

基本上，您已经忘记返回递归的结果，因此代码会继续返回错误的内容。如果testVal % divVal == 0，则该数字为非素数，因此您返回零。另外，不要使用仅取零或一的值的整数;使用boolean。

使用递归方法[java]识别素数

1 个答案: