HDU 1200 To and Fro

To and Fro

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 6409    Accepted Submission(s): 4400

Problem Description

Mo and Larry have devised a way of encrypting messages. They first decide secretly on the number of columns and write the message (letters only) down the columns, padding with extra random letters so as to make a rectangular array of letters. For example, if the message is “There’s no place like home on a snowy night” and there are five columns, Mo would write down

t o i o y
h p k n n
e l e a i
r a h s g
e c o n h
s e m o t
n l e w x


Note that Mo includes only letters and writes them all in lower case. In this example, Mo used the character ‘x’ to pad the message out to make a rectangle, although he could have used any letter.

Mo then sends the message to Larry by writing the letters in each row, alternating left-to-right and right-to-left. So, the above would be encrypted as

toioynnkpheleaigshareconhtomesnlewx

Your job is to recover for Larry the original message (along with any extra padding letters) from the encrypted one.

 

Input

There will be multiple input sets. Input for each set will consist of two lines. The first line will contain an integer in the range 2. . . 20 indicating the number of columns used. The next line is a string of up to 200 lower case letters. The last input set is followed by a line containing a single 0, indicating end of input.

 

Output

Each input set should generate one line of output, giving the original plaintext message, with no spaces.

 

Sample Input

5toioynnkpheleaigshareconhtomesnlewx3ttyohhieneesiaabss0

 

Sample Output

theresnoplacelikehomeonasnowynightxthisistheeasyoneab

 

Source

East Central North America 2004

这个题总体来说挺水的，但要是细节扣不好，也是很难的。在网上看了一下别人优秀的代码，恩，感觉DP不错。代码付下，声明，dp的代码不是小编的。

 1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4  5 using namespace std; 6  7 char ch[210]; 8 char dp[110][20]; 9 10 int main ()11 {12     int n;13     while (~scanf("%d",&n),n)14     {15         scanf("%s",ch);16         int x=0,y=0;17         int len=strlen(ch);18         for (int i=0; i<len; i++)19         {20             dp[x][y]=ch[i];21             if (x%2==0)22             {23                 y++;24                 if (y==n)25                 {26                     x++;27                     y--;28                 }29             }30             else31             {32                 y--;33                 if (y==-1)34                 {35                     x++;36                     y++;37                 }38             }39 40         }41         for (int i=0; i<n; i++)42         {43             for (int j=0; j<x; j++)44             {45                 printf ("%c",dp[j][i]);46             }47         }48         printf ("\n");49     }50     return 0;51 }

下面这个代码是我写的

#include <stdio.h>#include <string.h>int main(){char str[205];char map[205][205];int i,j,peace,n,cnt,index;while(scanf("%d",&n),n){scanf("%s",str);cnt=strlen(str);index=0;peace=1;for(i=0;i<cnt/n;i++){if(peace==1){for(j=0;j<n;j++){map[i][j]=str[index++];}}else{for(j=n-1;j>=0;j--){map[i][j]=str[index++];}}peace=peace*(-1);}for(j=0;j<n;j++){for(i=0;i<cnt/n;i++){printf("%c",map[i][j]);}}putchar('\n');}return 0;}