算法: 二叉树增、删、查、找

最近写个任务与二叉树相关。

这里记录一下二叉树相关代码。后续可以使用。

#include <stdio.h>
#include <string.h>

struct Node{
    Node *left;
    Node *right;
    int key;
};

Node* create_node(const int key){
    Node *tmp = new Node;
    tmp->left = NULL;
    tmp->right = NULL;
    tmp->key = key;
    return tmp;
}

Node* search_node(Node *node, const int key){
    if (node == NULL){
        return NULL;    
    }   
    
    Node *tmp = node;
    while(tmp != NULL){
        if (tmp->key == key){
            break;
        }   
        else{
            tmp = (tmp->key < key)? tmp->right:tmp->left;
        }   
    }   

    return tmp;
}

void insert_node(Node **root, const int key){
    if (*root == NULL){
        *root = create_node(key);
        return;
    }   

    Node *pre = NULL;
    Node *tmp = *root;

    while(tmp != NULL){
        if (tmp->key == key){
            return;
        }
        else{
            pre = tmp;
            tmp = (tmp->key < key)? tmp->right:tmp->left;
        }
    }

    tmp = create_node(key);
    if (pre->key < key){
        pre->right = tmp;
    }
    else {
        pre->left = tmp;
    }
    return;
}

void del_node(Node** root, int val){
    Node* pre = NULL;
    Node* curr = *root;
    while(curr && curr->key != val){
        pre = curr;
        curr = (val <= curr->key) ? curr->left:curr->right;
    }   

    if (curr == NULL){
        printf("delete node not exist\n");
        return ;
    }   

    if (curr->left == NULL && curr->right == NULL){ //删除节点是叶子节点
        if (pre == NULL){
            Node* tmp = *root;
            delete *root;
            *root = NULL;
        }   
        else {
            if (pre->left == curr){
                pre->left = NULL;
            }   
            else {
                pre->right = NULL;
            }   
            delete curr;
        }   
    }   
    else if (curr->left == NULL || curr->right == NULL){    //删除节点只有一个孩子节点
        if (curr->left != NULL){    //如果只存在left节点
            if(pre == NULL){
                *root = curr->left;
            }   
            else {
                if (pre->left == curr){
                    pre->left = curr->left;
                }   
                else {
                    pre->right = curr->left;
                }
            }
            delete curr;
        }
        else{   //如果只存在right节点
            if (pre == NULL) {
                *root = curr->right;
            }
            else {
                if (pre->right == curr){
                    pre->left = curr->right;
                }
                else{
                    pre->right = curr->right;
                }
            }
            delete curr;
        }
    }
    else if (curr->left != NULL && curr->right != NULL){    //删除节点left, right都存在
        Node* pp = curr;
        Node* p  = curr->right;
        while(p->left != NULL){
            pp = p;
            p  = p->left;
        }

        curr->key = p->key;
        if (curr == pp){
            curr->right = p->right;
        }
        else{
            pp->left = p->right;
        }
        delete p;
    }

    return ;
}

void del_tree(Node *root){
    if (root->left != NULL){
        del_tree(root->left);
    }

    if (root->right != NULL){
        del_tree(root->right);
    }

    if (root){
        delete root;
    }
}

int main(){
    Node *root = NULL;
    int cmd_no;
    int key;
    while(true){
        printf("items list:\n");
        printf("1. Search\n");
        printf("2. Insert\n");
        printf("3. Delete\n");
        printf("4. Quit\n");
        printf("input cmd:");

        scanf("%d", &cmd_no);
        if (cmd_no == 4){
            break;
        }
        scanf("%d", &key);
        switch(cmd_no){
            case 1:{
                if (search_node(root, key)){
                    printf("exist\n");
                }
                else {
                    printf("not exist\n");
                }
                break;
            }
            case 2:{
                insert_node(&root, key);
                break;
            }
            case 3:{
                del_node(&root, key);
                break;
            }
            default: {
                printf("input error");
            }
        }
    }

    del_tree(root);
    return 0;
}