题解 | #字符串加密#

#include<stdio.h>

int main() {
	char key[101] = { '0' };
	char sec[101] = { '0' };
	while (scanf("%s\n%s", &key, &sec) != EOF)
	{
		int len = strlen(key);	//密钥长度
		int seclen = strlen(sec);	//密码长度
		int num[26] = { 0 };	//原26字母出现标志组-出现则标1		
		char newkey[26] = { '0' };	//加密字母表
		int m = 0;	//加密字母表序号
		int index = 0;	//字母转换值（-'A'）
		char newsec[101] = { '0' };	//加密后字符串
		//1.密钥全部转为大写
		for (int i = 0; i < len; i++) 
		{
			key[i] = toupper(key[i]);
		}

		//2.密钥有该字母则标记为1，并按序存入加密字母表，不重复存
		for (int i = 0; i < len; i++)
		{	
			index = key[i] - 'A';	//字母序号
			if (num[index] == 0) {		
				num[index] = 1;		//该字母出现则表内置1
				newkey[m++] = key[i];	//按序存入加密字母表中
			}
		}

		//3.存剩余未出现的字母入加密字母表中
		for (int i = 0; i < 26; i++)
		{
			if (num[i] != 1) {
				newkey[m++] = i + 'A';
			}
		}		

		//4.字符串加密

		for (int i = 0; i < seclen+1; i++) 
		{
			if (sec[i] >= 'A' && sec[i] <= 'Z') 
			{
				index = sec[i] - 'A';
				newsec[i] = toupper(newkey[index]);
			}
			else if (sec[i] >= 'a' && sec[i] <= 'z') 
			{
				index = sec[i] - 'a';
				newsec[i] = tolower(newkey[index]);
			}
		}
		for (int i = 0; i < seclen; i++)
		{
			printf("%c", newsec[i]);
		}
		printf("\n");
	}
	return 0;
}