Java算法比赛常用方法实例总结

public static void main(String[] args) {
        String list="12321";
        StringBuilder str=new StringBuilder(list);
        if (str.reverse().toString().equals(list)){
            System.out.println(true);
        }
    }

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Map<String, Integer>map=new HashMap<>();
        Scanner sca=new Scanner(System.in);
        int n=sca.nextInt();
        sca.nextLine();
        for(int i=0;i<n;i++) {
            String str=sca.nextLine();
            int num=map.getOrDefault(str, 0)+1;
            map.put(str, num);
        }
        List<Map.Entry<String, Integer>>list=new ArrayList<>();
        for(Map.Entry<String, Integer>mv:map.entrySet()) {
            list.add(mv);
        }
        Collections.sort(list,new Comparator<Map.Entry<String, Integer>>() {

            @Override
            public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
                // TODO Auto-generated method stub
                return o2.getValue()-o1.getValue();
            }
        });
        System.out.println();
        for(int i=0;i<list.size();i++) {
            Map.Entry<String, Integer> mvEntry=list.get(i);
            String key=mvEntry.getKey();
            Integer value=mvEntry.getValue();
            System.out.println(value +" - "+ key);
        }
    }
}