根据出现次数按升序对数组进行排序

Question

如何根据java中按升序排列的值的数量排列数组中的元素.

这就是我尝试过的:

int a[]={0,0,0,1,3,3,2,1,3,5,6,0};
int b=a.length;
for(int i=0;i<b;i++) {
    for(int j=0;j<i;j++) {
        int temp;
        if( a[j]>a[i]) {
            temp=a[i];
            a[i]=a[j];
            a[j]=temp;
        }
    }
}

for(int r=0;r<a.length;r++) {
    System.out.println(a[r]);
}

Answer 1

这是使用TreeMap执行此操作的有效方法.

import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;

public class FrequencySort {
    public static void main(String[] args) {
        int[] ar = new int[] {5,2,8,8,5,5,8,1,9,0,1,1,0,1};

        Map<Integer,Integer> numbers = new HashMap<>();

        for(int number : ar) {
            if(numbers.containsKey(number)) {
                Integer  count = numbers.get(number);
                numbers.put(number, ++count);
            } else {
                numbers.put(number,1);
            }
        }

        final class FrequencyComparator implements Comparator<Integer> {
            Map<Integer,Integer> refMap;
            public FrequencyComparator(Map<Integer,Integer> base) {
                this.refMap = base;
            }

            @Override
            public int compare(Integer k1, Integer k2) {
                Integer val1 = refMap.get(k1);
                Integer val2 = refMap.get(k2);

                int num = val1.compareTo(val2)  ;
                // if frequencies are same then compare number itself
                return  num == 0 ? k1.compareTo(k2)   : num;
            }
        }

        FrequencyComparator comp = new FrequencyComparator(numbers);
        TreeMap<Integer,Integer> sortedMap = new TreeMap<Integer,Integer>(comp);
        sortedMap.putAll(numbers);
        for(Integer i : sortedMap.keySet()) {
            int frequencey = sortedMap.get(i);
            for(int count  = 1 ; count <= frequencey ; count++) {
                System.out.print(i + " " );
            }
        }
    }
}

Answer 2

这是一种让您开始的方法，它的基础是对映射中初始数组中每个整数发生了多少次的计数。计算完所有数字后，请按升序对地图进行排序，然后打印地图的输出：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.TreeMap;

public class SortCount {
    public static void main(String[] args) {
        int nums[] = {0,0,0,1,3,3,2,1,3,5,6,0};
        HashMap<Integer,Integer> counts = new HashMap<Integer,Integer>();

        for(int i = 0; i < nums.length; i++) {
            if(counts.containsKey(nums[
                Integer c = counts.get(nums[i]) + 1;
                counts.put(nums[i], c);
            }
            else {
                counts.put(nums[i],1);
            }
        }

        ValueComparator<Integer,Integer> bvc = new ValueComparator<Integer,Integer>(counts);
        TreeMap<Integer,Integer> sortedMap = new TreeMap<Integer,Integer>(bvc);
        sortedMap.putAll(counts);

        ArrayList<Integer> output = new ArrayList<Integer>();
        for(Integer i : sortedMap.keySet()) {
            for(int c = 0; c < sortedMap.get(i); c++) {
                output.add(i);
            }
        }

        System.out.println(output.toString());
    }
}

它使用一个Comparator类来比较中的值Map：

import java.util.Comparator;
import java.util.Map;

public class ValueComparator<T1,T2 extends Comparable<T2>> implements Comparator<T1> {
    Map<T1,T2> base;
    public ValueComparator(Map<T1,T2> base) {
        this.base = base;
    }

    @Override
    public int compare(T1 k1, T1 k2) {
        T2 val1 = base.get(k1);
        T2 val2 = base.get(k2);

        return val1.compareTo(val2);
    }
}