Question

问题： 任何正整数都可以表示为素数的唯一乘积，也称为素数因子分解。例如： 60 = 2 ^ 2 * 3 * 5

编写一个程序来计算正整数的素数分解。

输入：单个整数n，其中n≥2。

输出：格式为“p ^ a * q ^ b * ...”的字符串，其中p和q为素数，a和b为指数。如果指数为1，则应省略它。

我还有其他一切，我只需要找到一种方法将其放入“p ^ a * q ^ b * ...”形式。

这是我的代码：

import java.util.Scanner;

public class PrimeFactorization {
public static void main(String[] args) {

     // Input: A single integer, n, where n is greater than or equal to 2.

     System.out.println("Please input an integer greater than or equal to two!");
     System.out.println("This number will be factored.");
     Scanner inputNum = new Scanner(System.in);
     int toBFactored = inputNum.nextInt();

     // If the input does not fit the requirements, ask again for an input.

     while (toBFactored < 2) {
          System.out.println("Please input an integer greater than or equal to two.");
          toBFactored = inputNum.nextInt();
     }

     // Output: A string with the format: "p^a * q^b * ...", where p and q are
     // primes, and a and b are exponents. 
     // Decide first if a number (testNum) is prime.

     int primedecider = 0;
     for (int testNum = 2; testNum < toBFactored; testNum ++) {
          for (int factor = 2; factor < testNum; factor ++) {
               if (testNum % factor != 0 || testNum == 2) {
                    // Do nothing if prime.
               } else {
                    primedecider += 1;
                    // Add if composite.
               }
          }

          // If testNum is prime, if primedecider = 0, test if testNum divides
          // evenly into toBFactored.

          while (primedecider == 0 && toBFactored % testNum == 0 {
               System.out.print(testNum + " ");
               toBFactored /= testNum;
          }
     }
     System.out.print(toBFactored);

     inputNum.close();
}
}

120的输出是“2 2 2 3 5”。我怎么把它变成2 ^ 3 * 3 * 5？

Answer 1

如果不使用System.out.println打印因子，如果你把它们放在一个列表中然后这些函数将按照您描述的方式格式化它们。这当然只是众多方法中的一种。

private String formatFactors(List<Integer> factors) {
    StringBuilder builder = new StringBuilder();

    int prev = factors.get(0);
    int power = 1;
    int factor = prev;

    for (int i = 1; i < factors.size(); ++i) {
        factor = factors.get(i);
        if (factor == prev) {
            ++power;
        } else {
            appendFactor(builder, prev, power);
            prev = factor;
            power = 1;
        }
    }
    appendFactor(builder, factor, power);

    return builder.substring(3);
}

private void appendFactor(StringBuilder builder, int factor, int power) {
    builder.append(" * ").append(factor);
    if (power > 1) {
        builder.append("^").append(power);
    }
}

Java中基本素数因子化与指数

1 个答案: