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。

转载于:https://www.cnblogs.com/MXang/p/9219992.html

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