JAVA中的素數因子

Question

我正在嘗試編寫一個程序，它可以將輸出作爲給定數字的素數分解。但是，我的代碼作爲"2**2**2**2**2**5**7**7**11*"的輸出提供了正確的答案，但我希望它的具體輸出爲"(p1**n1)(p2**n2)...(pk**nk)"。這裏是我的代碼：

public class PrimeDecomp 
{ 
    public static String factors(int n) 
    { 
     String ans = ""; 
     for (int i = 2; i <= n; i++) 
     { 
      if (n % i == 0) 
      { 
       // checks if i is a divisor of num 
       ans += i + "**"; 
       // writes i in prime factorization 
       n = n/i; 
       // since it is written down, num=num/i 
       i--; 
       // just in case their are multiple factors of same number. 
       // For example, 12=2*2*3 
      } 
     } 
     return (ans.substring(0, ans.length() - 1)); 
    } 

    public static void main(String[] args) 
    { 
     System.out.println(PrimeDecomp.factors(86240)); 
    } 
} 

Answer 1

你幾乎得到它，而不是在一個時間計算的一​​個因素，計算所有相同的因素並計數：

public static String factors(int n) 
{ 
    String ans = ""; 
    int count = 0; 
    for (int i = 2; i <= n; i++) 
    { 
     // Reset the counter 
     count = 0; 

     /* 
     * Instead of only processing on factor, we process them all and 
     * count them 
     */ 
     while (n % i == 0) 
     { 
      count++; 
      n = n/i; 
     } 

     // If we have at least processed one add it to the string 
     if (count == 1) 
     { 
      ans += "(" + i + ")"; 
     } else if (count > 0) 
     { 
      ans += "(" + i + "**" + count + ")"; 
     } 
    } 
    return ans; 
} 

既然你是經常操作字符串在一個循環中，你應該使用StringBuilder