Trie Implementation in C++

问题

I am trying to implement the trie as shown on the TopCoder page. I am modifying it a bit to store the phone numbers of the users. I am getting segmentation fault. Can some one please point out the error.

 #include<iostream>
 #include<stdlib.h>
 using namespace std;

 struct node{
int words;
int prefix;
long phone;
struct node* children[26];
 };

struct node* initialize(struct node* root) {
    root = new (struct node);   
    for(int i=0;i<26;i++){
    root->children[i] = NULL;
    }
    root->word = 0;
    root->prefix = 0;
    return root;
 }

int getIndex(char l) {
    if(l>='A' && l<='Z'){
    return l-'A';
    }else if(l>='a' && l<='z'){
    return l-'a';
    }
 }

  void add(struct node* root, char * name, int data) {

    if(*(name)== '\0') {
        root->words = root->words+1;
        root->phone = data;
    } else {        
        root->prefix = root->prefix + 1;
        char ch = *name;
        int index = getIndex(ch);
        if(root->children[ch]==NULL)    {
            struct node* temp = NULL;
            root->children[ch] = initialize(temp);
        }
        add(root->children[ch],name++, data);
    }
 }

 int main(){
     struct node* root = NULL;
     root = initialize(root);
     add(root,(char *)"test",1111111111);
     add(root,(char *)"teser",2222222222);
         cout<<root->prefix<<endl;
     return 0;
  }

Added a new function after making suggested changes:

 void getPhone(struct node* root, char* name){
     while(*(name) != '\0' || root!=NULL) {
         char ch = *name;
         int index = getIndex(ch);
         root = root->children[ch];
         ++name;
     }
     if(*(name) == '\0'){
         cout<<root->phone<<endl;
     }
 }

回答1:

Change this:

add(root->children[ch], name++, data);
// ---------------------^^^^^^

To this:

add(root->children[ch], ++name, data);
// ---------------------^^^^^^

The remainder of the issues in this code I leave to you, but that is the cause of your run up call-stack.

EDIT OP ask for further analysis, and while I normally don't do so, this was a fairly simple application on which to expand.

This is done in several places:

 int index = getIndex(ch);
 root = root->children[ch];
 ... etc. continue using ch instead of index

It begs the question: "Why did we just ask for an index that we promptly ignore and use the char anyway?" This is done in add() and getPhone(). You should use index after computing it for all peeks inside children[] arrays.

Also, the initialize() function needs to be either revamped or outright thrown out in favor of a constructor-based solution, where that code truly belongs. Finally, if this trie is supposed to be tracking usage counts of words generated and prefixes each level is participating in, I'm not clear why you need both words and prefix counters, but in either case to update the counters your recursive decent in add() should bump them up on the back-recurse.

来源：https://stackoverflow.com/questions/16124056/trie-implementation-in-c

标签

c++

data-structures

segmentation-fault

trie