POJ 1056 IMMEDIATE DECODABILITY（字典树，判断有没有一个是另一个的前缀）

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最新推荐文章于 2020-11-13 21:49:15 发布

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本文介绍了一种用于判定一组二进制编码是否为立即码的方法。通过构建字典树（Trie），该算法能够高效地检查是否存在一个编码是另一个编码的前缀。文中详细解释了算法流程，并提供了一个完整的C++实现示例。

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IMMEDIATE DECODABILITY

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 8895		Accepted: 4222

Description

An encoding of a set of symbols is said to be immediately decodable if no code for one symbol is the prefix of a code for another symbol. We will assume for this problem that all codes are in binary, that no two codes within a set of codes are the same, that each code has at least one bit and no more than ten bits, and that each set has at least two codes and no more than eight.

Examples: Assume an alphabet that has symbols {A, B, C, D}

The following code is immediately decodable:
A:01 B:10 C:0010 D:0000

but this one is not:
A:01 B:10 C:010 D:0000 (Note that A is a prefix of C)

Input

Write a program that accepts as input a series of groups of records from standard input. Each record in a group contains a collection of zeroes and ones representing a binary code for a different symbol. Each group is followed by a single separator record containing a single 9; the separator records are not part of the group. Each group is independent of other groups; the codes in one group are not related to codes in any other group (that is, each group is to be processed independently).

Output

For each group, your program should determine whether the codes in that group are immediately decodable, and should print a single output line giving the group number and stating whether the group is, or is not, immediately decodable.

Sample Input

Sample Output

Set 1 is immediately decodable
Set 2 is not immediately decodable

Source

Pacific Northwest 1998

字典树基本的练习题。

判断立即码。

就是找有没有一个是另一个的前缀哦

//POJ 1056 IMMEDIATE DECODABILITY
//就是看有没有字符串是另一个的前缀
//立即码(也叫异前置码)

#include<stdio.h>
#include<stdlib.h>
#include<iostream>
#include<algorithm>
#include<string.h>
using namespace std;
const int MAX=2;
typedef struct Trie_Node
{
    bool isCode;
    struct Trie_Node *next[MAX];
}Trie;
bool flag;

void insert(Trie *root,char *str)
{
    Trie *p=root;
    int i=0;
    while(str[i]!='\0')
    {
        if(p->next[str[i]-'0']==NULL)
        {
            Trie *temp=new Trie;
            for(int j=0;j<MAX;j++)
              temp->next[j]=NULL;
            temp->isCode=false;
            p->next[str[i]-'0']=temp;
        }
        else
        {
            if(p->next[str[i]-'0']->isCode)
            {
                flag=false;
                return;
            }
        }
        p=p->next[str[i]-'0'];
        i++;
    }
    p->isCode=true;

}
void del(Trie *root)
{
    for(int i=0;i<MAX;i++)
      if(root->next[i]!=NULL)
        del(root->next[i]);
    free(root);
}
int main()
{
   // freopen("in.txt","r",stdin);
  //  freopen("out.txt","w",stdout);
    char str[20];
    int iCase=0;
    while(scanf("%s",&str)!=EOF)
    {
        iCase++;
        Trie *root=new Trie;
        for(int i=0;i<MAX;i++)
            root->next[i]=NULL;
        root->isCode=false;
        flag=true;
        insert(root,str);
        while(scanf("%s",&str))
        {
            if(strcmp(str,"9")==0)break;
            if(flag) insert(root,str);
        }
        if(flag)printf("Set %d is immediately decodable\n",iCase);
        else printf("Set %d is not immediately decodable\n",iCase);
        del(root);
    }
    return 0;
}