Question

我尝试使用递归创建二叉搜索树。我只写出了插入和搜索功能。但是，我的搜索功能有问题。我已经停留在第39行，如果我找不到树中存在的值，它就不会向我返回未找到该值的消息。请帮忙！

#include <stdio.h>
#include <stdlib.h>


typedef struct node { 
    int key; 
    struct node* left;
    struct node* right;
}node;

struct node* root= NULL;

int contains(node* temp, int el){

        if (el==temp->key) {
            return 1;
        }
        else if(el< temp->key) return contains(temp->left, el);
        else return contains(temp->right, el);
}

void searchPrompt(void){
    int el=-1;
    do{
        printf("   Search key or press -1 to return to menu: ");
        scanf("%d", &el);
        if(el>0){
            if (root==NULL) printf("\tError: tree is empty\n"); 
            else {
                if(contains(root, el)) printf("\tKey %d is found\n",el);
                else printf("\tKey %d is not found\n",el);
            }
        }
        else if (el<-1||el==0) printf("\tError: key not positive\n");
    }while (el!=-1);
    printf("   <Exit search method>\n\n");
}
//for search

void preOrder(node* temp){

    if (temp!=NULL){
        printf("%d ",temp->key);
        preOrder(temp->left);
        preOrder(temp->right);
    }
}

//for insertion
void insertNode(node* current, int value){        
        if(value< current->key){
            if (current->left == NULL) {
                current->left=(node*) malloc(sizeof(node));
                current->left->key = value;
                printf("\tSuccess! Value inserted: %d\n", current->left->key);

            }
            else {
                insertNode(current->left, value);
            }
        }
        else {
            if (current->right == NULL) {
                current->right=(node*) malloc(sizeof(node));
                current->right->key = value;
                printf("\tSuccess! Value inserted: %d\n", current->right->key);
            }
            else {
                insertNode(current->right, value);
            }
        }
}//end insert

void insert(int value){

    if(root==NULL){  //empty tree
        root =(node*) malloc(sizeof(node));

        root->key= value;
        printf("\tPrint root here: %d\n", value);
        root->left= NULL;
        root->right=NULL;
        printf("\tSuccess! Value inserted: %d\n", root->key);
    }
    else {
        insertNode(root, value);
    }        
        printf("\tResult: ");
        preOrder(root);
        printf("\n");
}

void insertPrompt(void){
    int value=-1;
    do{
        printf("   Insert value or press -1 to return to menu:  ");
        scanf("%d", &value);
        if(value>0)
            insert(value);
        else if (value<=0)printf("\tError: key not positive\n");
    }while (value!=-1);
    printf("   <Exit insert method>\n\n");

}

int menuPrompt(void){
    int choice=-1;
    do{
        printf("Enter <1> Search <2> Insert <3> Delete <4> Print Tree <5> Quit: ");
        scanf("%d", &choice);
        if(choice>5 || choice<1) printf("Error: invalid input! \n\n");
    }  while(choice>5 || choice<1);
    return choice;

}

int main(int argc, char *argv[]){
   int choice=-1;
   int value=-1;


    while(choice!=5){

   choice=menuPrompt();

   switch(choice){
    case 1:
         searchPrompt();
         break;
    case 2:
         insertPrompt();
         break;
    case 3:

         break;
    case 4:

         break;    
    case 5:
         printf("<Exit program> \n");
         break;
   }//end switch

}

  system("PAUSE");  
  return 0;
}

Answer 1

int contains(node* temp, int el){
        if(temp==NULL) return 0;
        if (el==temp->key) {
            return 1;
        }
        else if(el< temp->key) return contains(temp->left, el);
        else return contains(temp->right, el);
}

这解决了问题..如果没有找到，则会从UB中拯救你，也会解决错误的行为。

在 BLUEPIXY 中提到左右集合将新节点插入NULL。

为什么需要你可能会问......但事情就是你什么时候找不到一个元素最终你会到达一些叶节点。然后你会的向左或向右转，如果将其设置为NULL，则会调用contain 以NULL作为参数，然后它将按预期返回0 是

Answer 2

//for insertion
void insertNode(node* current, int value){        
        if(value< current->key){
            if (current->left == NULL) {
                current->left=(node*) malloc(sizeof(node));
                current->left->key = value;
                current->left->left = NULL;
                current->left->right = NULL;
                printf("\tSuccess! Value inserted: %d\n", current->left->key);

            }
            else {
                insertNode(current->left, value);
            }
        }
        else {
            if (current->right == NULL) {
                current->right=(node*) malloc(sizeof(node));
                current->right->key = value;
                current->right->left = NULL;
                current->right->right = NULL;
                printf("\tSuccess! Value inserted: %d\n", current->right->key);
            }
            else {
                insertNode(current->right, value);
            }
        }
}//end insert

这是我需要对新节点的左右两侧做什么的吗？ @BLUEPIXY @coderredoc

如果找不到值，则C-搜索中的二进制搜索树无法返回消息

2 个答案: