数据结构树遍历

#include <stdio.h>

#include <stdlib.h>



struct node {

   int data;



   struct node *leftChild;

   struct node *rightChild;

};



struct node *root = NULL;



void insert(int data) {

   struct node *tempNode = (struct node*) malloc(sizeof(struct node));

   struct node *current;

   struct node *parent;



   tempNode->data = data;

   tempNode->leftChild = NULL;

   tempNode->rightChild = NULL;



   //if tree is empty

   if(root == NULL) {

      root = tempNode;

   } else {

      current = root;

      parent = NULL;



      while(1) {

         parent = current;



         //go to left of the tree

         if(data < parent->data) {

            current = current->leftChild;                



            //insert to the left

            if(current == NULL) {

               parent->leftChild = tempNode;

               return;

            }

         }  //go to right of the tree

         else {

            current = current->rightChild;



            //insert to the right

            if(current == NULL) {

               parent->rightChild = tempNode;

               return;

            }

         }

      }            

   }

}



struct node* search(int data) {

   struct node *current = root;

   printf("Visiting elements: ");



   while(current->data != data) {

      if(current != NULL)

         printf("%d ",current->data);



      //go to left tree

      if(current->data > data) {

         current = current->leftChild;

      }

      //else go to right tree

      else {                

         current = current->rightChild;

      }



      //not found

      if(current == NULL) {

         return NULL;

      }

   }



   return current;

}



void pre_order_traversal(struct node* root) {

   if(root != NULL) {

      printf("%d ",root->data);

      pre_order_traversal(root->leftChild);

      pre_order_traversal(root->rightChild);

   }

}



void inorder_traversal(struct node* root) {

   if(root != NULL) {

      inorder_traversal(root->leftChild);

      printf("%d ",root->data);          

      inorder_traversal(root->rightChild);

   }

}



void post_order_traversal(struct node* root) {

   if(root != NULL) {

      post_order_traversal(root->leftChild);

      post_order_traversal(root->rightChild);

      printf("%d ", root->data);

   }

}



int main() {

   int i;

   int array[7] = { 27, 14, 35, 10, 19, 31, 42 };



   for(i = 0; i < 7; i++)

      insert(array[i]);



   i = 31;

   struct node * temp = search(i);



   if(temp != NULL) {

      printf("[%d] Element found.", temp->data);

      printf("\n");

   }else {

      printf("[ x ] Element not found (%d).\n", i);

   }



   i = 15;

   temp = search(i);



   if(temp != NULL) {

      printf("[%d] Element found.", temp->data);

      printf("\n");

   }else {

      printf("[ x ] Element not found (%d).\n", i);

   }            



   printf("\nPreorder traversal: ");

   pre_order_traversal(root);



   printf("\nInorder traversal: ");

   inorder_traversal(root);



   printf("\nPost order traversal: ");

   post_order_traversal(root);       



   return 0;

}