【Codeforces 922D】Robot Vacuum Cleaner

【链接】 我是链接,点我呀:)
【题意】

让你把n个字符串重新排序,然后按顺序连接在一起
使得这个组成的字符串的"sh"子序列最多

【题解】

        /*
         * 假设A的情况好于B
         * 也就对应了A排在B的前面
         * 那么
         * As*Bh>Ah*Bs ①
         * 现在假设B又比C来得好
         * 那么有
         * Bs*Ch>Bh*Cs ②
         * 由①可得
         * As/Ah>Bs/Bh
         * 由②可得
         * Bs/Bh>Cs/Ch
         * 那么有
         * As/Ah>As/Ch
         * 即As*Ch>Ah*As
         * 也就是说A排在C的前面比较优秀
         * 也就是说这个大小关系有传递性
         * 那么就直接排个序就好啦,按照两两之间排序的规则来写个比较函数就好了。
         */

StringBuilder比直接用字符串的"+"来得快

【代码】

import java.io.*;
import java.util.*;

public class Main {
    
    
    static InputReader in;
    static PrintWriter out;
        
    public static void main(String[] args) throws IOException{
        //InputStream ins = new FileInputStream("E:\\rush.txt");
        InputStream ins = System.in;
        in = new InputReader(ins);
        out = new PrintWriter(System.out);
        //code start from here
        new Task().solve(in, out);
        out.close();
    }
    
    static int N = (int)1e5;
    static class Task{
        
        class Pair{
            int s,h,i;
            public Pair(int s,int h,int i) {
                this.s = s;
                this.h = h;
                this.i = i;
            }
        }
        
        public void solve(InputReader in,PrintWriter out) {
            Pair a[] = new Pair[N+10];
            String s[] = new String[N+10];
            int n;
            n = in.nextInt();
            for (int i = 1;i <= n;i++) {
                s[i] = in.next();
                int ss = 0,hh = 0;
                for (int j = 0;j < (int)s[i].length();j++) {
                    char key = s[i].charAt(j);
                    if (key=='s') ss++;
                    if (key=='h') hh++;
                }
                a[i] = new Pair(ss,hh,i);
            }
            Arrays.sort(a, 1,n+1,new Comparator<Pair>() {

                @Override
                public int compare(Pair A, Pair B) {
                    // TODO Auto-generated method stub
                    long As,Ah,Bs,Bh;
                    As = A.s;Ah = A.h;
                    Bs = B.s;Bh = B.h;
                    long temp1 =As*Bh;long temp2 =Ah*Bs;
                    if (temp1>temp2) {
                        return -1;
                    }else if (temp1==temp2) {
                        return 0;
                    }else {
                        return 1;
                    }
                }
                
            });
            StringBuilder sb = new StringBuilder();
            for (int i = 1;i <= n;i++) {
                sb.append(s[a[i].i]);
            }
            String v = sb.toString();
            n = v.length();
            long ans = 0;
            long cnts = 0;
            for (int i = 0;i < n;i++) {
                if (v.charAt(i)=='s') {
                    cnts++;
                }else if (v.charAt(i)=='h'){
                    ans = ans + cnts;
                }
            }
            out.println(ans);
        }
    }

    

    static class InputReader{
        public BufferedReader br;
        public StringTokenizer tokenizer;
        
        

        

        
        public InputReader(InputStream ins) {
            br = new BufferedReader(new InputStreamReader(ins));
            tokenizer = null;
        }
        
        public String next(){
            while (tokenizer==null || !tokenizer.hasMoreTokens()) {
                try {
                tokenizer = new StringTokenizer(br.readLine());
                }catch(IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }
        
        public int nextInt() {
            return Integer.parseInt(next());
        }
    }
}