java面试常见算法总结

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java面试常见算法总结

1、 一个int[]数组 如何打印出重复次数前5的元素及重复次数

/**
 * 排序
 * @author v_liuwen
 * @date 2019/3/5
 */
public class SortDemo {

    public static void main(String[] args) {
        int[] nums = new int[]{1,3,7,4,9,2,3,4,3,4,5,3,6,3,7,5,4,5,6,7,9,4};
        sort(nums);
    }


    public static void sort(int[] nums){
        Map<Integer,Integer> map = new HashMap<>();
        Arrays.stream(nums).forEach(num ->{
            if(map.get(num)==null){
                map.put(num,1);
            }else {
                map.put(num,map.get(num)+1);
            }
        });

        map.forEach((k,v) ->{
            System.out.println("key:"+k+"  value:"+v);
        });


        //按键排序
//        System.out.println("---------------按键排序--------------------");
//        Map<Integer,Integer> resultKey = map.entrySet()
//                .stream().sorted(Map.Entry.comparingByKey())
//                .collect(Collectors.toMap(Map.Entry::getKey,Map.Entry::getValue,(oldValue,newValue) ->oldValue,LinkedHashMap::new));
//        System.out.println(resultKey);
        //按值排序
        System.out.println("---------------按值排序--------------------");
        Map<Integer,Integer> resultValue = map.entrySet()
                .stream().sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
                .collect(Collectors.toMap(Map.Entry::getKey,Map.Entry::getValue,(oldValue,newValue) ->oldValue,LinkedHashMap::new));
        Integer count = 5;
        for(Integer key:resultValue.keySet()){
            if(count<1){
                break;
            }
            System.out.println("key:"+key+"   value:"+resultValue.get(key));
            count--;
        }
    }
}

打印结果

key:1  value:1
key:2  value:1
key:3  value:5
key:4  value:5
key:5  value:3
key:6  value:2
key:7  value:3
key:9  value:2
---------------按值排序--------------------
key:3   value:5
key:4   value:5
key:5   value:3
key:7   value:3
key:6   value:2

持续更新中。。。