TRIE树

一个能够实现查找元素、增加元素和删除元素三种操作的数据结构称为字典。TRIE树，又称键树，可以用来构造字典，适合所有元素都是由字母和数字标记的情形。下面是TRIE树的一种C＋＋实现：

#include <stdio.h>
#include <iostream>
#include <string.h>

using namespace std;
const int num_chars = 26;

class Trie {
protected:
struct Trie_node {
char* word;
Trie_node* branch[num_chars];
Trie_node();
};
Trie_node* root;

public:
Trie();
int search(const char* word) const;
int insert(const char* word);
int remove(const char* word);

void printall(char *pre, Trie_node *p);
void printpre(char *pre);
};

Trie::Trie():root(NULL)
{
}

Trie::Trie_node::Trie_node()
{
word = NULL;
for (int i=0; i<num_chars; ++i)
branch[i] = NULL;
}

int Trie::search(const char* word) const
{
char char_code;
Trie_node *location = root;

while( location!=NULL && *word!=0 ) {
if (*word>='A' && *word<='Z')
char_code = *word-'A';
else if (*word>='a' && *word<='z')
char_code = *word-'a';
else
return 0;

location = location->branch[char_code];
word++;
}
if ( location != NULL && location->word != NULL ) {
return 1;
} else
return 0;
}

int Trie::insert(const char* word)
{
int result = 1;
if ( root == NULL ) root = new Trie_node;
char char_code;
Trie_node *location = root;

while( location!=NULL && *word!=0) {
if (*word>='A' && *word<='Z')
char_code = *word-'A';
else if (*word>='a' && *word<='z')
char_code = *word-'a';
else
return 0;

if( location->branch[char_code] == NULL )
location->branch[char_code] = new Trie_node;
location = location->branch[char_code];
word++;
}
if (location->word != NULL)
result = 0;
else {
location->word = new char[strlen(word)+1];
strcpy(location->word, word);
}
return result;
}

int Trie::remove(const char* word)
{
int result = 1;
char char_code;
Trie_node *location = root;

while( location!=NULL && *word!=0) {
if (*word>='A' && *word<='Z')
char_code = *word-'A';
else if (*word>='a' && *word<='z')
char_code = *word-'a';
else
return 0;

location = location->branch[char_code];
word++;
}
if (location) {
delete location->word;
location->word = NULL;
} else {
result = 0;
}
return result;
}

void Trie::printall(char *pre, Trie_node *p)
{
if (p->word != NULL) {
cout<<pre<<endl;
}

for (int i=0; i<num_chars; ++i) {
if (p->branch[i] != NULL) {
char ch = 'a' + i;
char *prestr = (char *)malloc(strlen(pre)+2);
sprintf(prestr, "%s%c", pre, ch);
printall(prestr, p->branch[i]);
free(prestr);
}
}
}

void Trie::printpre(char *pre)
{
char char_code;
char *p = pre;
Trie_node *location = root;

while( location!=NULL && *pre!=0 ) {
if (*pre>='A' && *pre<='Z')
char_code = *pre-'A';
else if (*pre>='a' && *pre<='z')
char_code = *pre-'a';
else
return;

location = location->branch[char_code];
pre++;
}

if (location != NULL)
printall(p, location);

return;
}

int main(int argc, char *argv[])
{
Trie t;

t.insert("liu");
t.insert("aigui");
t.insert("liuag");
t.insert("china");
t.insert("trie");

t.remove("aigui");
t.remove("abc");
t.printpre("");

if (t.search(argv[1]))
cout<<argv[1]<<" was found"<<endl;
else
cout<<argv[1]<<" was not found"<<endl;

if (argv[2])
t.printpre(argv[2]);

return 0;
}

(刘爱贵 / Aiguille LIU)