codeforce R 491 (div2)

本来打完就想写的，，奈何舍友要睡了，我开个台灯感觉怪怪的，就没写。

A题竟然一开始wa了。。。后来发现对于c和a还有c和b的关系没有判断，，丢掉了很多罚时。

B题我的方法是    计算 sum，然后 分别统计 2、3、4的个数，一个一个试，具体看代码(前面快速io有点长见谅

package R491;
 
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.StringTokenizer;
 
public class Main2 {
    static BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
    static StringTokenizer tok;
    static boolean hasNext()
    {
        while(tok==null||!tok.hasMoreTokens())
            try{
                tok=new StringTokenizer(in.readLine());
            }
            catch(Exception e){
                return false;
            }
        return true;
    }
    static String next()
    {
        hasNext();
        return tok.nextToken();
    }
    static long nextLong()
    {
        return Long.parseLong(next());
    }
    static int nextInt()
    {
        return Integer.parseInt(next());
    }
    static PrintWriter out=new PrintWriter(new OutputStreamWriter(System.out));
 
    public static void main(String[] args) {
        int n = nextInt();
        int a[] = new int[n];
        int b[] = new int[8];
        int sum = 0;
        for(int i=0;i<n;i++){
            a[i] = nextInt();
            b[a[i]]++;
            sum+=a[i];
        }
        int num = 0;
        while (sum<4.5*n){
            if (b[2]>0){
                sum+=3;
                b[2]--;
                num++;
            }else if (b[3]>0){
                sum+=2;
                b[3]--;
                num++;
            }else if (b[4]>0){
                sum+=1;
                b[4]--;
                num++;
            }
        }
        out.print(num);
        out.flush();
    }
}

　　

C 一开始还以为可能有点意思，然后二分板子就出来了，没啥可说的，中间竟然wa了一发，，很玄学，   ，判断时 如果 把  num1>=num2  写成 num1>=(double)n/2 就会wa。。。

package R491;
 
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.StringTokenizer;
 
public class Main3 {
    static BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
    static StringTokenizer tok;
    static boolean hasNext()
    {
        while(tok==null||!tok.hasMoreTokens())
            try{
                tok=new StringTokenizer(in.readLine());
            }
            catch(Exception e){
                return false;
            }
        return true;
    }
    static String next()
    {
        hasNext();
        return tok.nextToken();
    }
    static long nextLong()
    {
        return Long.parseLong(next());
    }
    static int nextInt()
    {
        return Integer.parseInt(next());
    }
    static PrintWriter out=new PrintWriter(new OutputStreamWriter(System.out));
 
    static long n;
    public static void main(String[] args) {
        n = nextLong();
        long l = 1;
        long r = n;
        while (l<=r){
            long mid=(l+r)/2;
            if (caneat(mid)){
                r=mid-1;
            }else {
                l=mid+1;
            }
        }
        out.print(l);
        out.flush();
    }
    public static boolean caneat(long k){
        long num=0;
        long num2 = 0;
        long temp = n;
        while (temp>0){
            if (temp<k){
                num+=temp;
                break;
            }
            num+=k;
            temp-=k;
            num2+=(temp/10);
            temp-=temp/10;
        }
        if (num>=num2){
            return true;
        }else {
            return false;
        }
    }
}

　　

D题就很和蔼可亲了，竟然只有两行，直接暴力，我的方法是  umm懒得说看代码吧

package R491;
 
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.StringTokenizer;
 
public class Main4 {
    static BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
    static StringTokenizer tok;
    static boolean hasNext()
    {
        while(tok==null||!tok.hasMoreTokens())
            try{
                tok=new StringTokenizer(in.readLine());
            }
            catch(Exception e){
                return false;
            }
        return true;
    }
    static String next()
    {
        hasNext();
        return tok.nextToken();
    }
    static long nextLong()
    {
        return Long.parseLong(next());
    }
    static int nextInt()
    {
        return Integer.parseInt(next());
    }
    static PrintWriter out=new PrintWriter(new OutputStreamWriter(System.out));
 
    public static void main(String[] args) {
        String s[] = new String[2];
        for(int i=0;i<2;i++){
            s[i] = next();
        }
        if (s[0].length()==1){
            out.print(0);
            out.flush();
            return;
        }
        char ch1[] = s[0].toCharArray();
        char ch2[] = s[1].toCharArray();
        int ans = 0;
        for(int i=0;i<ch1.length;i++){
            if (ch1[i]=='0'&&ch2[i]=='0'){
                if (i==0){
                    if (ch1[i+1]=='0'){
                        ans++;
                        ch1[i+1]='X';
                        ch1[i]=ch2[i]='X';
                    }else if (ch2[i+1]=='0'){
                        ans++;
                        ch2[i+1]='X';
                        ch1[i]=ch2[i]='X';
                    }
                }else if (i<ch1.length-1){
                    if (ch1[i-1]=='0'){
                        ans++;
                        ch1[i-1]='X';
                        ch1[i]=ch2[i]='X';
                    }else if (ch2[i-1]=='0'){
                        ans++;
                        ch2[i-1]='X';
                        ch1[i]=ch2[i]='X';
                    }else if (ch1[i+1]=='0'){
                        ans++;
                        ch1[i+1]='X';
                        ch1[i]=ch2[i]='X';
                    }else if (ch2[i+1]=='0'){
                        ans++;
                        ch2[i+1]='X';
                        ch1[i]=ch2[i]='X';
                    }
                }else if (i== ch1.length-1) {
                    if (ch1[i - 1] == '0') {
                        ans++;
                        ch1[i - 1] = 'X';
                        ch1[i] = ch2[i] = 'X';
                    } else if (ch2[i - 1] == '0') {
                        ans++;
                        ch2[i - 1] = 'X';
                        ch1[i] = ch2[i] = 'X';
                    }
                }
            }
        }
        out.print(ans);
        out.flush();
    }
}

　　E 啊哈哈哈哈，尴尬而不失礼貌的微笑，因为我太弱了又很垃圾还是一个数学白痴所以我没写出来。。。

　　F学长都没写。。。学长51分钟过掉ABCDE好像就开始挂机了，发现F有点难就睡觉去了，然后D题掉了，囍。

　　近期：补一下排列组合，抓紧学个tarjan把前天的E题补掉。(对不起是我太弱了不会tarjan

　　rating:1548

　　忽然发现今晚还有一场，我可能要1600+了欸嘿嘿嘿。