查找字典中某个公共前缀的所有单词

//Trie.h/* * trie树统计公共前缀的单词集合、个数 */#include <set>#include <string>using namespace std;#define BRANCH 26struct Node{Node * next[BRANCH];int prefix; // 此前缀的单词个数,为验证结果而加bool isStr;Node():prefix(0), isStr(false){memset(next, 0, sizeof(next));}};class Trie{private:Node * root;set<string> * preSet;    /* private: * DFS() and freeNextArr() are private functions */* DFS find all the words from Node "ptr" * 实际就是寻找“以当前前缀本身为单词”的单词 */void DFS(Node * ptr, string preStr){for(int i = 0; i < BRANCH; ++i){if(ptr->next[i] != NULL){char chr[] = {'a' + i, '\0'};DFS(ptr->next[i],preStr+string(chr));}if(ptr->isStr)  // 存在当前前缀的单词{this->preSet->insert(preStr);}}}// free the next arrayvoid freeNextArr(Node * ptr){for(int i = 0; i < BRANCH; ++i){if(ptr->next[i] != NULL){freeNextArr(ptr->next[i]);}}delete ptr;}public:Trie(){root = new Node();preSet = new set<string> ();}// insert a wordvoid insert(const char * word){if(NULL == word){return ;}Node * ptr = root;while(*word){if(ptr->next[*word-'a'] == NULL){ptr->next[*word-'a'] = new Node();}ptr->prefix ++;ptr = ptr->next[*word-'a'];++word;}ptr->isStr = true;}// find the location of the wordNode * search(const char * word){if(NULL == word){return NULL;}Node * ptr = root;while(ptr && *word){ptr = ptr->next[*word-'a'];++word;}return ptr;}// find the common prefix words setset<string> * findCommonPrefix_Set(const char * prefix){if(NULL == prefix){return NULL;}Node * ptr = search(prefix); // find location of prefixif(ptr == NULL)              // prefix not exist{return NULL;}DFS(ptr, string(prefix));   // DFS find commonPre wordsreturn this->preSet;}// clear the preSetvoid clearPreSet(){this->preSet->clear();}// free the memoryvoid freeMemory(){this->freeNextArr(root);delete this->preSet;}};



测试程序：

#include <iostream>#include "Trie.h"void main(){Trie comPreTrie;comPreTrie.insert("abc");comPreTrie.insert("abcd");comPreTrie.insert("abcde");comPreTrie.insert("abcdef");comPreTrie.insert("abcdefg");comPreTrie.insert("cde");/* test the common prefix "abcd" * 注，测试时默认输入合法字符，即 a-z *    本文程序不对此做出检查 */Node * ptr = comPreTrie.search("abcd");if(ptr){printf("num of words prefix by \"abcd\" is %d\n",ptr->isStr ? ptr->prefix + 1 : ptr->prefix);}else{printf("ptr for \"abcd\" is null\n");}set<string> * comPreSet= comPreTrie.findCommonPrefix_Set("abcd");if(comPreSet){for(set<string>::iterator it = comPreSet->begin();it != comPreSet->end(); ++it){printf("%s\n", (*it).c_str());}}else{printf("comPreSet for \"abcd\" is null\n");}comPreTrie.clearPreSet();printf("---------------\n");/* test the common prefix "word" */ptr = comPreTrie.search("word");if(ptr){printf("num of words prefix by \"word\" is %d\n",ptr->isStr ? ptr->prefix + 1 : ptr->prefix);}else{printf("ptr for \"word\" is null\n");}comPreSet = comPreTrie.findCommonPrefix_Set("word");if(comPreSet){for(set<string>::iterator it = comPreSet->begin();it != comPreSet->end(); ++it){printf("%s\n", (*it).c_str());}}else{printf("comPreSet for \"word\" is null\n");}comPreTrie.clearPreSet();// free memorycomPreTrie.freeMemory();}