题目：给你一些01串，判断是不是某些串是其它串的前缀。

分析：字符串，字典树。

            首先，将字符串按长度排序，这样前缀一定在前面；

            然后，再插入字典树的过程中，判断是否覆盖即可。

说明：注意数组的大小。

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>

using namespace std;

char words[1004][104];

/* Trie define */  
#define nodesize 20002      //节点个数   
#define dictsize 2          //字符集大小   

typedef struct node1  
{  
    int    flag;            //值域   
    node1* next[dictsize];  
}tnode;  
tnode  dict[nodesize];  
int    ID[256];  

class Trie  
{  
    private: 
		int    sub;
        int    size;  
        int    count;
        tnode* root;  
    public:  
        Trie() {makeID(); initial();}  
        void makeID() {ID['0'] = 0;ID['1'] = 1;}  
        void initial() {  
            memset( dict, 0, sizeof( dict ) ); 
            count=0;size=0;sub=0;root=newnode();  
        }  
        tnode* newnode() {return &dict[size ++];}  
        void insert( char* word ) {  
            tnode* now = root;  
            for ( int i = 0 ; word[i] ; ++ i ) {
                if ( !now->next[ID[word[i]]] )  
                    now->next[ID[word[i]]] = newnode();  
                if ( now->flag ) sub = 1;
                now = now->next[ID[word[i]]];  
            }
			if ( now->flag ++ ) sub = 1;
        }
        int query() {return sub;}
}trie;  
/* Trie  end */  

int cmp( const void* a, const void *b )
{
	return strlen((char *)a) - strlen((char *)b);
}

int main()
{
	int Case = 1;
	while ( ~scanf("%s",words[0]) ) {
		
		trie.initial();
		int count = 1;
		while ( words[count-1][0] != '9' ) 
			scanf("%s",words[count ++]);
		qsort( words, count-1, sizeof(words[0]), cmp );
		
		for ( int i = 0 ; i < count-1 ; ++ i )
			trie.insert( words[i] );
		
		printf("Set %d is ",Case ++);
		if ( trie.query() ) printf("not ");
		printf("immediately decodable\n");
	}
	return 0;
}