插入功能到AVL树中不会插入

Question

I am working on an avl tree with strings as keys. The print statements indicate that the insert is happening but in the testing function it reports that the left and right nodes of the root remain null.

Here is my avl tree code:

#include "AVLAdt.h"

void printVal(node * toPrint){
    printf("\n node value: %s\n", toPrint->nodeValue);
}

node * search(node * root, char * searchVal){
    if(isExternal(root) == 1) return NULL;
    if(strcmp(searchVal,root->nodeValue)<0){
        return(search(root->leftNode,searchVal));
    }
    else if(strcmp(searchVal,root->nodeValue)==0){
        return(root);
    }
    else {
        return(search(root->rightNode,searchVal));
    }
}



/*initialize a node*/   
node * initNode(char * toAdd){
    node * newNode = malloc(sizeof(node));
    strcpy(newNode->nodeValue, toAdd);
    newNode->leftNode = NULL;
    newNode->rightNode = NULL;
    newNode->height = 1;
    return newNode;
}



/*function to insert a new node into tree and rebalance if necessary*/
node * insert(node * root, char * newValue){


    if(root == NULL){
        printf("\n Inserting %s. \n", newValue);
        return(initNode(newValue));

    }
    else{

        if(strcmp(newValue,root->nodeValue)<0){
            printf("go left");
            insert(root->leftNode, newValue);
        }
        else if(strcmp(newValue,root->nodeValue)>0){
            printf("go to right node of %s", root->nodeValue);
            insert(root->rightNode, newValue);
        }
        else{
            root->count++;
            return (root);
        }
    }

Testing program:

#include "AVLAdt.h"

int main(){


    node * root = NULL;

    char * testString = malloc(sizeof(char)*50);
    strcpy(testString, "aa");

    char * testString1 = malloc(sizeof(char)*50);
    strcpy(testString1, "bb");


    printf("does it try to insert?");

    root = insert(root, testString);
    root = insert(root, testString1);

    printVal(root);

    if(getRight(root) == NULL) printf("right is null");
    else{

        printf("right is");
        printVal(getRight(root));
    }

    if(getLeft(root) == NULL) printf("left is null");
    else{

        printf("left is");
        printVal(getRight(root));
    }



    return(0);
}

The code returns that both left and right nodes of "aa" are null. Why is this?

Answer 1

In the search() function, not sure why you do

if(isExternal(root) == 1) return NULL;

If the node is external, ie doesn't have any leaves, you'd still want to compare its nodeValue to the searchVal and return root in case of match.

In initNode() function, next-to-the-last line should be

newNode->count = 1;

instead of

newNode->height = 1;

Also, it seems to me that in the insert() function, initNode() 's return value should be assigned to root to store the pointer to the newly added node in the tree, ie you should have:

return root = initNode(newValue);

instead of

return(initNode(newValue));

(you also don't have to put return value in parenthesis by the way).

WhozCraig has already pointed out issue with the return values of recursive insert() calls.