华为OD机考题(基础API)

基础API

字典排序

List<String> list=new ArrayList();
//add list member
Arrays.sort(list);

List<Map<String,Integer>> list=new ArrayList();
//add list member
Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
   @Override
   public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2{
        return o2.getValue()-o1.getValue();
   }
});

进制转换

Integer.parseInt(hexString, 16)//16进制转10进制

Integer.toBinaryString(num);//十进制转二进制

int decimal = Integer.parseInt(binaryString, 2);//二进制转10进制

>> 有符号右移

>>>无符号右移

bit处理​​​​​​

​Integer.bitCount(n);//二进制中1的个数

字典排序示例:

package huaweiod;

import java.util.*;

public class Test{
    public static void main(String[] args) throws Exception{
        Map<String,Map<String,Integer>> map=new HashMap();
        Map<String,Integer> map1=new HashMap();
        map1.put("004",160);
        map1.put("003",150);
        map1.put("002",150);
        map1.put("001",160);
        map1.put("005",150);
        map.put("02",map1);

        Map<String,Integer> map2=new HashMap();
        map2.put("003",130);
        map2.put("004",140);
        map.put("01",map2);

        Set<String> classNum=map.keySet();
        Object[] array=classNum.toArray();
        Arrays.sort(classNum.toArray());
        for(Object o:array){
            System.out.println("class:"+o);
            HashMap<String,Integer> tempMap=(HashMap)map.get(o);
            List<Map.Entry<String,Integer>> list=new ArrayList(tempMap.entrySet());
            Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
                @Override
                public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
                    return o2.getValue()-o1.getValue();
                }
            });
            for(Map.Entry<String,Integer> entry:list){
                System.out.println(entry.getKey()+":"+entry.getValue());
            }
        }
    }
}