计算一个数的每个质因数的个数

Question

我想计算一个整数的每个质因数的个数，然后打印出最大的个数。例如720 = 2^4 * 3^2 * 5^1。所以我想打印 Maximum Number of Time occurrence = 4 并且数字是 2。我尝试使用 Integer.max()，但那没有用。

import java.util.Scanner;
import java.util.TreeMap;

public class Main {

    public static void main(String[] args) {
        int num;
        Scanner in = new Scanner(System.in);
        System.out.print("Enter a number: ");
        num = in.nextInt();
        TreeMap<Integer, Integer> factors = new TreeMap<>();

        for (int i =2; i < num; i++){
            int count = 0;
            while (num%i == 0){
                System.out.println(i + " ");
                num = num/i;
                count ++;
            }
            if (count > 0){
                factors.put(i, count);
            }
        }
        if (num > 2){
            System.out.println(num + " ");
            factors.put(num, 1);
        }

        System.out.println( "-------------" );
        for( Integer factor : factors.keySet() ){
            System.out.println( factor + "^" + factors.get( factor ) );
        }
    }
}

Answer 1

如果您只想要出现次数最多的素数，那么您可以在每个素数都经过测试后进行检查。为此，地图并不是真正必要的。请注意，多个素数可能出现相同的次数。如果有平局，这只保存遇到的第一个。

int num;
Scanner in = new Scanner(System.in);
System.out.print("Enter a number: ");
num = in.nextInt();
int primeFactor = 0;
int count = 0;
int maxCount = 0;
int inc = 1; // initial increment.
int i = 2;   // intitial prime
while (num > 1) {
    count = 0;
    while (num%i == 0) {
        num = num/i;
        count++;
    }

    // here check current count against maxCount and
    // alter if required.
    if (count > maxCount) {
       maxCount = count;
       primeFactor = i;
    }
    if (count > 0) {
        System.out.printf("Prime = %d, count = %d%n", i, count);
    }
    i+=inc;  // bump by 1 to get 3 and then
    inc = 2; // start incrementing by 2
}

// and print the results.
System.out.println("First highest occuring prime = " + primeFactor);
System.out.println("MaxCount = " + maxCount);

计算一个数的每个质因数的个数

count the number of each prime factor of a number

java

prime-factoring