The Decoder

欢迎访问我的新博客：http://www.milkcu.com/blog/

原文地址：http://www.milkcu.com/blog/archives/uva458.html

题目描述

 The Decoder 

Write a complete program that will correctly decode a set of characters into a valid message. Your program should read a given file of a simple coded set of characters and print the exact message that the characters contain. The code key for this simple coding is a one for one character substitution based upon a single arithmetic manipulation of the printable portion of the ASCII character set.

Input and Output

For example: with the input file that contains:

1JKJ'pz'{ol'{yhklthyr'vm'{ol'Jvu{yvs'Kh{h'Jvywvyh{pvu5
1PIT'pz'h'{yhklthyr'vm'{ol'Pu{lyuh{pvuhs'I|zpulzz'Thjopul'Jvywvyh{pvu5
1KLJ'pz'{ol'{yhklthyr'vm'{ol'Kpnp{hs'Lx|pwtlu{'Jvywvyh{pvu5

your program should print the message:

*CDC is the trademark of the Control Data Corporation.
*IBM is a trademark of the International Business Machine Corporation.
*DEC is the trademark of the Digital Equipment Corporation.

Your program should accept all sets of characters that use the same encoding scheme and should print the actual message of each set of characters.

Sample Input

1JKJ'pz'{ol'{yhklthyr'vm'{ol'Jvu{yvs'Kh{h'Jvywvyh{pvu5
1PIT'pz'h'{yhklthyr'vm'{ol'Pu{lyuh{pvuhs'I|zpulzz'Thjopul'Jvywvyh{pvu5
1KLJ'pz'{ol'{yhklthyr'vm'{ol'Kpnp{hs'Lx|pwtlu{'Jvywvyh{pvu5

Sample Output

*CDC is the trademark of the Control Data Corporation.
*IBM is a trademark of the International Business Machine Corporation.
*DEC is the trademark of the Digital Equipment Corporation.

解题思路

首先，编写一个小程序，获得解吗规则。

#include <stdio.h>
int main(void) {
	char s1[] = "1JKJ'pz'{ol'{yhklthyr'vm'{ol'Jvu{yvs'Kh{h'Jvywvyh{pvu5";
	char s2[] = "*CDC is the trademark of the Control Data Corporation.";
	int i = 0;
	while(s1[i] != '') {
		printf("%4d%4d
", s1[i], s2[i]);
		i++;
	}
	return 0;
}

解码规则是ASCII码值减7。

代码实现

#include <stdio.h>
int main(void) {
	int c;
	while((c = getchar()) != EOF) {
		if(c == '
') {
			putchar('
');
		} else {
			putchar(c - 7);
		}
	}
	return 0;
}

（全文完）