> “The input consists of a number of sentences consisting only of characters p through z and N, C, D, E, and I。”去你的吧，明明会有其他字符出现，其他字符出现也算syntax error!!!!!!哥好好的算法就被这玩意儿骗了一次submission……算了，在POJ被骗submission习惯了，连连按两次submit都能被骗AC率……
> 
> 不谈，上代码。代码里有注释，可读性还是很强的，自己捉摸一下就明白原理了。
> 
> // p through z are equivalent, substitute them for 0; substitute N for 1; C, D, E, I are equivalent, substitute them for 2;
> // all the 1s do not count; leave them out;
> // the remaining strings of 0s and 2s, if justified, make up a non-prefix system
> #include <stdio.h>
> #include <string.h>
> 
> int main()
> {
> 	char st[300];
> 	int len;
> 	int num2, num0;
> 	int i;
> 	int flag;
> 	while (scanf("%s", st) != EOF)
> 	{
> 		len = strlen(st);
> 		num2 = 0;
> 		num0 = 0;
> 		i = len - 1;
> 		flag = 1;
> 		while ((i == len - 1) || (num2 + 1 <= num0) && (i >= 0))
> 		{
> 			if ((st[i] == 'C') || (st[i] == 'D') || (st[i] == 'E') || (st[i] == 'I'))
> 				num2++;
> 			else if ((st[i] >= 'p') && (st[i] <= 'z'))
> 				num0++;
> 			else if (st[i] == 'N')
> 				;
> 			else
> 				flag = 0; // the input sentence contains non-justified characters
> 			i--;
> 		}
> 		if ((flag == 1) && (num2 + 1 == num0))
> 			printf("YES\n");
> 		else
> 			printf("NO\n");
> 	}
> 	return 0;
> }