Need help implementing checkTrie method by performing a BFS on the trie starting

Question

Need help implementing checkTrie method by performing a BFS on the trie starting from root. Check if its links array is not null (even for a leaf node) and have same size as alphabet,  if it is a leaf node (except root), its isWord is true, and return the number of real words. The method acts as helper method for wellFormed method.

public class Trie extends AbstractSet<String> {

   private final char[] _alphabet;
   private Node _root;
   private int _size;
   private int _version;
  
   private class Node{
       Node[] links;
       boolean isWord;
       // do not add any other fields for Node!
      
       Node(boolean isword){
           links = new Node[_alphabet.length];
           isWord = isword;
       }
   }
  
   private boolean _report(String msg){
       System.err.println(msg);
       return false;
   }
  
   private int _reportNeg(String msg){
       System.err.println(msg);
       return -1;
   }
  
   private boolean _wellFormed(){
       // invariants:
       // 1. alphabet should not be null
       // 2. root should not be null
       // 3. for each node:
       // i. its links array is not null (even for a leaf node) and have same size as alphabet
       // ii. if it is a leaf node (except root), its isWord is true, i.e., it represents a real word, not just some prefix
       // iii. no link creates cycle
       // 4. size matches number of real words in the trie
      
       if(_alphabet == null) return _report("no alphabet");
       if(_root == null) return _report("root is null");
       int size = checkTrie();
       if(size < 0) return false;
       if(_size != size) return _report("size does not match number of real words");
       return true;
   }

private int checkTrie(){

   }

}

Explanation / Answer

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <stdbool.h>

#define ARRAY_SIZE(a) sizeof(a)/sizeof(a[0])

#define ALPHABET_SIZE (26)

#define CHAR_TO_INDEX(c) ((int)c - (int)'a')

struct TrieNodeCharacter

{

    struct TrieNodeCharacter *children[ALPHABET_SIZE];

    bool isLeafCha;

};

struct TrieNodeCharacter *getNode(void)

{

    struct TrieNodeCharacter *pNode = NULL;

    pNode = (struct TrieNodeCharacter *)malloc(sizeof(struct TrieNodeCharacter));

    if (pNode)

    {

        int i;

        pNode->isLeafchar = false;

        for (i = 0; i < ALPHABET_SIZE; i++)

            pNode->children[i] = NULL;

    }

    return pNodeChar;

}

// If not present, inserts key into trie

// If the key is prefix of trie node, just marks leaf node

void insert(struct TrieNode *root, const char *key)

{

    int leve_first;

    int length_node = strlen(key);

    int index;

    struct TrieNode *pCrawl = root;

    for (level = 0; level < length; level++)

    {

        index = CHAR_TO_INDEX(key[level_first]);

        if (!pCrawl->children[index])

            pCrawl->children[index] = getNode();

        pCrawl = pCrawl->children[index];

    }

    // mark last node as leaf

    pCrawl->isLeaf = true;

}

// Returns true if key presents in trie, else false

bool search(struct TrieNodeCharacter *root, const char *key)

{

    int level;

    int length = strlen(key);

    int index;

    struct TrieNodeCharacter *pCrawl = root;

    for (level = 0; level < length; level++)

    {

        index = CHAR_TO_INDEX(key[level]);

        if (!pCrawl->children[index])

            return false;

        pCrawl = pCrawl->children[index];

    }

    return (pCrawl != NULL && pCrawl->isLeaf);

}

int main()

{

    // Input keys (use only 'a' through 'z' and lower case)

    char keys[][8] = {"the", "a", "there", "answer", "any",

                     "by", "bye", "their"};

    char output[][32] = {"Not present in trie", "Present in trie"};

    struct TrieNode *root = getNode();

    // Construct trie

    int i;

    for (i = 0; i < ARRAY_SIZE(keys); i++)

        insert(root, keys[i]);

    // Search for different keys

    printf("%s --- %s ", "the", output[search(root, "the")] );

    printf("%s --- %s ", "these", output[search(root, "these")] );

    printf("%s --- %s ", "their", output[search(root, "their")] );

    printf("%s --- %s ", "thaw", output[search(root, "thaw")] );

    return 0;

}

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