【ACM】杭电1200:To and Fro

这道题非常有意思。我们只需要按照题目的要求建立一个矩阵，然后按照指定的顺序遍历就OK啦。

步骤：获取暗文->还原矩阵->遍历矩阵->输出结果。

代码：

#include <stdio.h>
#include <string.h>

char word[110][30]; /* 存放字母矩阵 */

int main(int argc, char *argv[])
{
	int COL,ROW,len,r;
	char ch[250];
	char str[250]; /* 存放重组好的句子 */
	while(scanf("%d",&COL) != EOF && COL != 0)
	{
		memset(str,0,sizeof(str));
		memset(ch,0,sizeof(ch));
		scanf("%s",ch);
		len = strlen(ch);
		if(0 == len % COL) /* 计算行数 */
		{
			ROW = len / COL;
		}
		else
		{
			ROW = (len / COL) + 1;
		}
		
		/* 还原矩阵 */
		int ix1 = 0;
		int row,col,direct = 1; /* 从左向右 */
		for(row = 1 ; row <= ROW ; ++row)
		{
			if(1 == direct)
			{
				for(col = 1 ; col <= COL ; ++col)
				{
					word[row][col] = ch[ix1++];
				}
				direct = -1; /* 改变方向 */
			}
			else if(-1 == direct) /* 从右向左 */
			{
				for(col = COL ; col >= 1 ; --col)
				{
					word[row][col] = ch[ix1++];
				}
				direct = 1;
			}
		}
		
		
		
		/* 重组字母 */
		int ix2 = 0;
		for(row = 1 ; row <= COL ; ++row)
		{
			for(col = 1 ; col <= ROW ; ++col)
			{
					str[ix2++] = word[col][row];
			}
		}

		printf("%s\n",str);
	}
	
	return 0;
}

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

5
toioynnkpheleaigshareconhtomesnlewx
3
ttyohhieneesiaabss
0

 

Sample Output

theresnoplacelikehomeonasnowynightx
thisistheeasyoneab