algorithm to print trie alphabetically

问题

I've been busy trying to code a trie ordered tree data structure in C. My program reads in words in a sentence one at a time from a .txt, then it stores each word in a trie without duplicates. It then grabs all other words in that sentence and stores them in a subtrie of the word that was stored. For example if we had the following sentence: "contribute to open source. " My code does the following...

            root
  ab'c'defghijklmn'o'pqr's''t'uvwxyz
    'o'           'p'   'o''o'-subtrie-> "contribute", "open", "source"
    'n'           'e'   'u'
    't'           'n'   'r'
    'r'                 'c'-subtrie->"contribute", "to", "open", 
    'i'                     
    'b'
    'u'
    't'
    'e'-subtrie-> "to", "open", "source"

I have successfully been able to insert words into the trie and also the subtries. I have thoroughly tested this so I am pretty confident everything works the way it was intended to. However, i cant seem to figure out the algorithem to print the trie and subtrie alphabetically.

Here's the struct i am using

typedef struct TrieNode
{
     // number of times this string occurs in the corpus
 int count;

// 26 TrieNode pointers, one for each letter of the alphabet
struct TrieNode *children[26];

// the co-occurrence subtrie for this string
struct TrieNode *subtrie;
} TrieNode;

here is the function i wrote to insert tries. The parameters are the root of the trie, a char array of the word i want to insert, size of the word i am inserting, z = -1 initially.

TrieNode *trieInsert(TrieNode *root, char *wordArray, int sizeOfWord, int z){

    z++;
    int x1, j, index; 
    char c1 = wordArray[z];     

    //INSERT char second level 
    // do alphaNum conversions and check uper or lower case for lev1Char
    x1 = char2Num(c1);
        if(x1 >26 ){
        printf("ERRRRRRRRRRRRRRRRRRrr:line475");
    return root;
    }

    //base case
    if( sizeOfWord == z ) 
    return root; 

    //check to see if we already inserted this 
    if( root->children[x1] == NULL ){ 

    //we insert second letter 
    root->children[x1] = malloc(sizeof(struct TrieNode) );
            root->children[x1]->subtrie = NULL;
    root->children[x1]->count = 0;  
    //set children of newly malloced to null 
    for(j = 0; j < 27; j++)
        root->children[x1]->children[j] = NULL;

    }

    //increment word count on last char of word 
    if((sizeOfWord - 1) == z) 
    root->children[x1]->count++;    

    return trieInsert(root->children[x1], wordArray, sizeOfWord, z);

}

Here is the code i cant figure out. It was to print the trie alphabetically, however, it's output is incorrect.

void printTrieAlefBet( TrieNode *root ){

    int i; 

    if( root->subtrie != NULL){
        printf(" (%d)", root->count);
        return;  
    }


    for( i = 0; i < 27; i++)
        if( root->children[i] != NULL){
            printTrieAlefBet(root->children[i]);
            printf("%c", num2Char(i, 0) );
        }


}

Any thoughts would be greatly appreciated!

回答1:

Got it to work. Here's the code.
Special thanks to prof Sean Szumlanski!

// Helper function called by `printTrie()`.
void printTrieHelper(TrieNode *root, char *buffer, int k)
{
    int i;
    if (root == NULL)
        return;

    if (root->count > 0)
        printf("%s (%d)\n", buffer, root->count);

    buffer[k + 1] = '\0';

    for (i = 0; i < 26; i++)
    {
        buffer[k] = 'a' + (i - 1);

        printTrieHelper(root->children[i], buffer, k + 1);
    }

    buffer[k] = '\0';
}

// If printing a subtrie, the second parameter should be 1; otherwise, 0.
void printTrie(TrieNode *root, int useSubtrieFormatting)
{
    char buffer[1026];

    if (useSubtrieFormatting)
    {
        strcpy(buffer, "- ");
        printTrieHelper(root, buffer, 2);
    }

    else
    {
        strcpy(buffer, 'and');
        printTrieHelper(root, buffer, 0);
    }
}

来源：https://stackoverflow.com/questions/17843628/algorithm-to-print-trie-alphabetically

标签

trie