java - 我如何知道一个数字出现在数组中的频率

Question

我处理将随机数列表保存在数组中，现在我有一个包含 7 个数字的数组:(3,4,6,6,10,3,5)，我想知道数字出现的频率是多少.
我试过这个，但我真的不知道怎么做

int size = 7
int aux [] = {3,4,6,6,10,3,5};
for(int i = 0 ; i<size; i++) {
            int cont = 0 ;
            for(int j = 0; i<size-1; j++) {
                if(aux[i] == aux[j+1]) {
                     aux[j+1] = -1;
                     cont++;
                } 
                
            }
            System.out.println("The number "+ aux[i] + " appears "+ cont + "times");
        }

Answer 1

您可以使用 Map 并在循环中自己计算出现次数:

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

public class Main {
    private static Map<Integer, Integer> getCounts(int[] arr) {
        Map<Integer, Integer> counts = new HashMap<>();
        for (int x : arr) {
            counts.put(x, counts.getOrDefault(x, 0) + 1);
        }
        return counts;
    }

    public static void main(String[] args) {
        int[] arr = {3, 4, 6, 6, 10, 3, 5};
        System.out.println(Arrays.toString(arr));
        Map<Integer, Integer> counts = getCounts(arr);
        for (Map.Entry<Integer, Integer> entry : counts.entrySet()) {
            System.out.printf("%d occurs %d %s\n", entry.getKey(), 
                entry.getValue(), entry.getValue() == 1 ? "time" : "times");
        }
    }
}

输出:

[3, 4, 6, 6, 10, 3, 5]
3 occurs 2 times
4 occurs 1 time
5 occurs 1 time
6 occurs 2 times
10 occurs 1 time