字典树

  1 #include <stdio.h>
  2 #include <stdlib.h>
  3 #include <string.h>
  4 
  5 #define ARRAY_SIZE(a) sizeof(a)/sizeof(a[0])
  6 
  7 // Alphabet size (# of symbols)
  8 #define ALPHABET_SIZE (26)
  9 
 10 // Converts key current character into index
 11 // use only ‘a‘ through ‘z‘ and lower case
 12 #define CHAR_TO_INDEX(c) ((int)c - (int)‘a‘)
 13 
 14 // trie node
 15 typedef struct trie_node trie_node_t;
 16 struct trie_node
 17 {
 18     int value;
 19     trie_node_t *children[ALPHABET_SIZE];
 20 };
 21 
 22 // trie ADT
 23 typedef struct trie trie_t;
 24 struct trie
 25 {
 26     trie_node_t *root;
 27     int count;
 28 };
 29 
 30 // Returns new trie node (initialized to NULLs)
 31 trie_node_t *getNode(void)
 32 {
 33     trie_node_t *pNode = NULL;
 34 
 35     pNode = (trie_node_t *)malloc(sizeof(trie_node_t));
 36 
 37     if (pNode)
 38     {
 39         int i;
 40 
 41         pNode->value = 0;
 42 
 43         for (i = 0; i < ALPHABET_SIZE; i++)
 44         {
 45             pNode->children[i] = NULL;
 46         }
 47     }
 48 
 49     return pNode;
 50 }
 51 
 52 // Initializes trie (root is dummy node)
 53 void initialize(trie_t *pTrie)
 54 {
 55     pTrie->root = getNode();
 56     pTrie->count = 0;
 57 }
 58 
 59 // If not present, inserts key into trie
 60 // If the key is prefix of trie node, just marks leaf node
 61 void insert(trie_t *pTrie, char key[])
 62 {
 63     int level;
 64     int length = strlen(key);
 65     int index;
 66     trie_node_t *pCrawl;
 67 
 68     pTrie->count++;
 69     pCrawl = pTrie->root;
 70 
 71     for (level = 0; level < length; level++)
 72     {
 73         index = CHAR_TO_INDEX(key[level]);
 74         if (!pCrawl->children[index])
 75         {
 76             pCrawl->children[index] = getNode();
 77         }
 78 
 79         pCrawl = pCrawl->children[index];
 80     }
 81 
 82     // mark last node as leaf
 83     pCrawl->value = pTrie->count;
 84 }
 85 
 86 // Returns non zero, if key presents in trie
 87 int search(trie_t *pTrie, char key[])
 88 {
 89     int level;
 90     int length = strlen(key);
 91     int index;
 92     trie_node_t *pCrawl;
 93 
 94     pCrawl = pTrie->root;
 95 
 96     for (level = 0; level < length; level++)
 97     {
 98         index = CHAR_TO_INDEX(key[level]);
 99 
100         if (!pCrawl->children[index])
101         {
102             return 0;
103         }
104 
105         pCrawl = pCrawl->children[index];
106     }
107 
108     return (0 != pCrawl && pCrawl->value);
109 }
110 
111 // Driver
112 int main()
113 {
114     // Input keys (use only ‘a‘ through ‘z‘ and lower case)
115     char keys[][8] = { "the", "a", "there", "answer", "any", "by", "bye", "their" };
116     
117     char output[][32] = { "Not present in trie", "Present in trie" };
118 
119     trie_t trie;
120     initialize(&trie);
121 
122     // Construct trie
123     for (int i = 0; i < ARRAY_SIZE(keys); i++)
124     {
125         insert(&trie, keys[i]);
126     }
127 
128     // Search for different keys
129     printf("%s --- %s\n", "the", output[search(&trie, "the")]);
130     printf("%s --- %s\n", "these", output[search(&trie, "these")]);
131     printf("%s --- %s\n", "their", output[search(&trie, "their")]);
132     printf("%s --- %s\n", "thaw", output[search(&trie, "thaw")]);
133 
134     return 0;
135 }