項目euler 7 - 我完全卡住了，無法弄清楚

Question

我一直在修補這個代碼幾個小時，我只是無法讓它輸出正確的答案。誰能告訴我我要去哪裏？此版本正在輸出104033

package Euler; 

public class prime100001 { 

    private static boolean isPrime(long num) { 
     if (num == 2 || num == 3){ 
      return true; 
     } 
     if (num % 2 == 0){ 
      return false; 
     } 
     for (int i = 3; i * i < num; i += 2){ 
      if (num % i == 0){ 
       return false; 
      } 
     } 
     return true; 
    } 

    public static void main (String [] args){ 

     int counter = 0; 
     int primenum = 1; 

     while(counter < 10001){ 
      primenum += 2; 
      if(isPrime(primenum)){ 
       counter ++; 
      } 
     } 
     System.out.println(primenum); 
    } 

} 

Answer 1

只是想確認一下，您是否打印10,001st素數？

public class prime100001 { 
    private static boolean isPrime(long num) { 
     if (num == 2 || num == 3){ 
      return true; 
     } 
     if (num % 2 == 0){ 
      return false; 
     } 
     for (int i = 3; (i * i) <= num; i += 1){ 
      // Changed the condition from < to <=, as you need to capture squares 
      // (e.g. when num = 9, original method will return false as i * i = 9 < 9 is false. 
      // Also changed the increment from 2 to 1. 
      if (num % i == 0){ 
       return false; 
      } 
     } 
     return true; 
    } 

    public static void main(String [] args){ 

     int counter = 0; 

     int lastPrime = 1; 
     while(counter < 10001){ 
      lastPrime += 1; 
      // Changed increment to include 2 in the count, plus 
      // not skipping any other ints to test. 
      if (isPrime(lastPrime)){ 
       counter++; 
      } 
     } 
     System.out.println(lastPrime); 
     // Shows 104,743 
     // 10,000th prime: https://primes.utm.edu/lists/small/10000.txt 
    } 
} 

希望這會有所幫助。 ;）