成绩分析：

import java.util.Scanner;


/**
样例
7
80
92
56
74
88
99
10
 *
 */
public class Main {

    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int minn = 10010;
        int maxn = 0;
        int n = sc.nextInt();
        sc.nextLine();
        long sumn = 0;
        for(int i=0;i<n;i++) {
            int temp = sc.nextInt();
            sc.nextLine();
            minn = Math.min(minn,temp);
            maxn = Math.max(maxn,temp);
            sumn += temp;
        }
        double avgn = sumn/(double)n;
        System.out.println(maxn);
        System.out.println(minn);
        System.out.printf("%.2f",avgn);
        
    }
}

字串分值：
快速构造arraylist：new ArrayList<Integer>(Arrays.asList(i+1))
遍历set：for(char c : s)

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;


//计算每个字符对结果的贡献
//贡献实际上和前后一个相同字符的位置有关
public class Main {

    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        //从1开始算，这样第一个减0就是我们需要的第一个乘数
        String str = sc.nextLine();
        Set<Character> s = new HashSet<Character>();
        HashMap<Character,ArrayList<Integer>> h = new HashMap<Character,ArrayList<Integer>>();
        for(int i=0;i<str.length();i++) {
            char c = str.charAt(i);
            s.add(c);
            if(h.containsKey(c)) {
                ArrayList<Integer> temp = h.get(c);
                temp.add(i+1);
            }
            else h.put(c, new ArrayList<Integer>(Arrays.asList(i+1)));
        }
        int res = 0;
        
        for(char c : s) {
            ArrayList<Integer> temp = h.get(c);
            for(int j=0;j<temp.size();j++) {
                int a1,a2;
                if(j==0)a1 = 0;
                else a1 = temp.get(j-1);
                if(j==temp.size()-1)a2 = str.length()+1;
                else a2 = temp.get(j+1);
                int mm = (temp.get(j)-a1)*(a2-temp.get(j));
                res += mm;
            }
        }
        
        System.out.println(res);
    }
}

回文日期
SimpleDateFormat format = new SimpleDateFormat("yyyyMMdd");
format.setLenient(false);
format.parse(idate);

import java.text.SimpleDateFormat;
import java.util.Scanner;

public class Main {
    static boolean isDate(String idate) {
        SimpleDateFormat format = new SimpleDateFormat("yyyyMMdd");
        try {
            format.setLenient(false);
            format.parse(idate);
        }catch(Exception e) {
            return false;
        }
        return true;
    }
    
    static boolean isABAB(String idate) {
        return idate.charAt(0)==idate.charAt(2) && idate.charAt(1)==idate.charAt(3);
    }
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        n /= 10000;
        String res1 = null;
        String res2 = null;
        for(int i=n+1;i<9999;i++) {
            StringBuilder sb = new StringBuilder(i+"");
            sb.reverse();
            String idate = i + "" + sb;
            if(res1!=null && res2!=null)break;
            if(isDate(idate)) {
                if(res1==null)res1 = idate;
                if(isABAB(idate)) {
                    res2 = idate;
                }
            }
        }
        
        System.out.println(res1);
        System.out.println(res2);
    }
}

递增序列：

public class Main {
    
    /*
VLPWJVVNNZSWFGHSFRBCOIJTPYNEURPIGKQGPSXUGNELGRVZAG
SDLLOVGRTWEYZKKXNKIRWGZWXWRHKXFASATDWZAPZRNHTNNGQF
ZGUGXVQDQAEAHOQEADMWWXFBXECKAVIGPTKTTQFWSWPKRPSMGA
BDGMGYHAOPPRRHKYZCMFZEDELCALTBSWNTAODXYVHQNDASUFRL
YVYWQZUTEPFSFXLTZBMBQETXGXFUEBHGMJKBPNIHMYOELYZIKH
ZYZHSLTCGNANNXTUJGBYKUOJMGOGRDPKEUGVHNZJZHDUNRERBU
XFPTZKTPVQPJEMBHNTUBSMIYEGXNWQSBZMHMDRZZMJPZQTCWLR
ZNXOKBITTPSHEXWHZXFLWEMPZTBVNKNYSHCIQRIKQHFRAYWOPG
MHJKFYYBQSDPOVJICWWGGCOZSBGLSOXOFDAADZYEOBKDDTMQPA
VIDPIGELBYMEVQLASLQRUKMXSEWGHRSFVXOMHSJWWXHIBCGVIF
GWRFRFLHAMYWYZOIQODBIHHRIIMWJWJGYPFAHZZWJKRGOISUJC
EKQKKPNEYCBWOQHTYFHHQZRLFNDOVXTWASSQWXKBIVTKTUIASK
PEKNJFIVBKOZUEPPHIWLUBFUDWPIDRJKAZVJKPBRHCRMGNMFWW
CGZAXHXPDELTACGUWBXWNNZNDQYYCIQRJCULIEBQBLLMJEUSZP
RWHHQMBIJWTQPUFNAESPZHAQARNIDUCRYQAZMNVRVZUJOZUDGS
PFGAYBDEECHUXFUZIKAXYDFWJNSAOPJYWUIEJSCORRBVQHCHMR
JNVIPVEMQSHCCAXMWEFSYIGFPIXNIDXOTXTNBCHSHUZGKXFECL
YZBAIIOTWLREPZISBGJLQDALKZUKEQMKLDIPXJEPENEIPWFDLP
HBQKWJFLSEXVILKYPNSWUZLDCRTAYUUPEITQJEITZRQMMAQNLN
DQDJGOWMBFKAIGWEAJOISPFPLULIWVVALLIIHBGEZLGRHRCKGF
LXYPCVPNUKSWCCGXEYTEBAWRLWDWNHHNNNWQNIIBUCGUJYMRYW
CZDKISKUSBPFHVGSAVJBDMNPSDKFRXVVPLVAQUGVUJEXSZFGFQ
IYIJGISUANRAXTGQLAVFMQTICKQAHLEBGHAVOVVPEXIMLFWIYI
ZIIFSOPCMAWCBPKWZBUQPQLGSNIBFADUUJJHPAIUVVNWNWKDZB
HGTEEIISFGIUEUOWXVTPJDVACYQYFQUCXOXOSSMXLZDQESHXKP
FEBZHJAGIFGXSMRDKGONGELOALLSYDVILRWAPXXBPOOSWZNEAS
VJGMAOFLGYIFLJTEKDNIWHJAABCASFMAKIENSYIZZSLRSUIPCJ
BMQGMPDRCPGWKTPLOTAINXZAAJWCPUJHPOUYWNWHZAKCDMZDSR
RRARTVHZYYCEDXJQNQAINQVDJCZCZLCQWQQIKUYMYMOVMNCBVY
ABTCRRUXVGYLZILFLOFYVWFFBZNFWDZOADRDCLIRFKBFBHMAXX
     */
    public static void main(String[] args) {
        int a = 2;
        int b = 4;
        Scanner sc = new Scanner(System.in);
        char[][] m = new char[a][b];
        for(int i=0;i<a;i++) {
            String str = sc.nextLine();
            for(int j=0;j<b;j++) {
                char c = str.charAt(j);
                m[i][j] = c;
            }
        }
        int res = 0;
        for(int i=0;i<a;i++) {
            for(int j=0;j<b;j++) {
                for(int k=i+1;k<a;k++) {
                    if(m[i][j]<m[k][j])res++;
                }
                for(int k=j+1;k<b;k++) {
                    if(m[i][j]<m[i][k])res++;
                }
                //右下
                for(int k=1;i+k<a&&j+k<b;k++) {
                    if(m[i][j]<m[i+k][j+k])res++;
                }
                //右上
                for(int k=1;i-k>=0&&j+k<b;k++) {
                    if(m[i][j]!=m[i-k][j+k])res++;
                }
            }
        }
        System.out.println(res);
    }
}

平方拆分

public class Main {
    static int res = 0;
    
    static void f(int n,int cur) {
        cur = cur+n*n;
        //System.out.println(cur);
        if(cur>2019)return;
        if(cur==2019)res++;
        for(int i=n+1;i<50;i++) {
            f(i,cur);
        }
        
    }
    
    public static void main(String[] args) {
        for(int i=1;i<50;i++) {
            f(i,0);
        }
        System.out.println(res);
    }
}res+=(s.size()-1);