[算法] avl树实现

大二的时候数据结构课死活没看懂的一个东东，看了2小时，敲了2小时，调了2小时。。。

平衡树某一节点的左右子树高度相差大于1的时候即需要调整，调整可分为四中情况 ll,rr,lr,rl其中lr,rl是由不同顺序的ll,rr来实现的，代码比想象的简短。

一棵平衡的树只有在插入和删除节点的时候，才会变的不平衡，所以掌握好时机，判断平衡是否破坏及不平衡的种类，再纠正即可

代码如下。。

avl.h

struct AVLNode {
    struct AVLNode *left;
    struct AVLNode *right;
    int data;
    int height;
};

static const int AVL_STATUS_OK = 0;
static const int AVL_STATUS_FOUNDED = 1;
static const int AVL_STATUS_NOTFOUNDED = 2;
static const int AVL_STATUS_FAILED = -1;

int avl_insert(struct AVLNode **root, int data);
int avl_find(struct AVLNode *root, int data);
int avl_del(struct AVLNode **root, int data);
int avl_del_tree(struct AVLNode *root);
void print_avl_tree(struct AVLNode *root);
int _get_height(struct AVLNode *node);
int _max(int a, int b);
void _single_rotate_left(struct AVLNode **node);
void _single_rotate_right(struct AVLNode **node);
void _double_rotate_left_right(struct AVLNode **node);
void _double_rotate_right_left(struct AVLNode **node);

　

avl.c

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

#include "avl.h"

int avl_insert(struct AVLNode **ptr_root, int data) {
    int ret;
    if(NULL == *ptr_root) {
        *ptr_root = malloc(sizeof(struct AVLNode));
        if(NULL == *ptr_root) {
            return AVL_STATUS_FAILED;
        }
        (*ptr_root)->data = data;
        (*ptr_root)->left = NULL;
        (*ptr_root)->right = NULL;
        (*ptr_root)->height = 0;
        return AVL_STATUS_OK;
    }

    if(data == (*ptr_root)->data) {
        return AVL_STATUS_OK;
    }
    else if(data < (*ptr_root)->data) {
        ret = avl_insert(&((*ptr_root)->left), data);
        if(_get_height((*ptr_root)->left) - _get_height((*ptr_root)->right) > 1){
            if(data < (*ptr_root)->left->data){
                _single_rotate_left(ptr_root);
            }
            else {
                _double_rotate_left_right(ptr_root);
            }
        }
    }
    else {
        ret = avl_insert(&((*ptr_root)->right), data);
        if(_get_height((*ptr_root)->right) - _get_height((*ptr_root)->left) > 1){
            if(data > (*ptr_root)->right->data) {
                _single_rotate_right(ptr_root);
            }
            else {
                _double_rotate_right_left(ptr_root);
            }
        }
    }
    (*ptr_root)->height = _max(_get_height((*ptr_root)->left), _get_height((*ptr_root)->right)) + 1;
    return ret;
}

int avl_find(struct AVLNode *root, int data) {
    if(NULL == root) {
        return AVL_STATUS_NOTFOUNDED;
    }
    if(data == root->data) {
        return AVL_STATUS_FOUNDED;
    }
    if(data < root->data) {
        return avl_find(root->left, data);
    }
    else {
        return avl_find(root->right, data);
    }
}

int avl_del(struct AVLNode **root, int data) {
    struct AVLNode *t;
    if(*root == NULL) {
        return AVL_STATUS_OK;
    }
    if(data < (*root)->data) {
        avl_del(&((*root)->left), data);
        if(_get_height((*root)->right) - _get_height((*root)->left) > 1){
            if((*root)->right->left != NULL && (_get_height((*root)->right->left) > _get_height((*root)->right->right))) {
                _double_rotate_right_left(root);
            }
            else {
                _single_rotate_right(root);
            }
        }
    }
    else if(data > (*root)->data) {
        avl_del(&((*root)->right), data);
        if(_get_height((*root)->left) - _get_height((*root)->right) > 1){
            if((*root)->left->right != NULL && (_get_height((*root)->left->right) > _get_height((*root)->left->left))) {
                _double_rotate_left_right(root);
            }
            else {
                _single_rotate_left(root);
            }
        }
    }
    else {
        if(NULL != (*root)->left && NULL != (*root)->right) {
            t = (*root) -> right;
            while(t->left != NULL) {
                t = t->left;
            }
            (*root) -> data = t->data;
            avl_del(&((*root)->right), t->data);
            if(_get_height((*root)->left) - _get_height((*root)->right) > 1){
            if((*root)->left->right != NULL && (_get_height((*root)->left->right) > _get_height((*root)->left->left))) {
                _double_rotate_left_right(root);
            }
            else {
                _single_rotate_left(root);
            }
        }
        }
        else {
            t = *root;
            if((*root)->left == NULL) {
                *root = (*root) -> right;
            }
            else if((*root)->right == NULL) {
                *root = (*root) -> left;
            }
            free(t);
        }
    }
    return AVL_STATUS_OK;
}

int avl_del_tree(struct AVLNode *root) {
    if(NULL == root) {
        return AVL_STATUS_OK;
    }
    avl_del_tree(root->left);
    avl_del_tree(root->right);
    free(root);
    return AVL_STATUS_OK;
}

int _get_height(struct AVLNode *node) {
    if(NULL == node){
        return -1;
    }
    else{
        return node->height;
    }
}

int _max(int a, int b) {
    return a > b ? a:b;
}

void _single_rotate_left(struct AVLNode **node) {
    struct AVLNode* root = *node;
    *node = root->left;
    root->left = (*node)->right;
    (*node)->right = root;
    root->height = _max(_get_height(root->left), _get_height(root->right)) + 1;
    (*node)->height = _max(_get_height((*node)->left), _get_height((*node)->right)) + 1;
}

void _single_rotate_right(struct AVLNode **node) {
    struct AVLNode* root = *node;
    *node = root->right;
    root->right = (*node)->left;
    (*node)->left = root;
    root->height = _max(_get_height(root->left), _get_height(root->right)) + 1;
    (*node)->height = _max(_get_height((*node)->left), _get_height((*node)->right)) + 1;
}

void _double_rotate_left_right(struct AVLNode **node) {
    struct AVLNode* root = *node;
    _single_rotate_right(&(root->left));
    _single_rotate_left(node);
}

void _double_rotate_right_left(struct AVLNode **node) {
    struct AVLNode* root = *node;
    _single_rotate_left(&(root->right));
    _single_rotate_right(node);
}

void print_avl_tree(struct AVLNode *node) {
    if(NULL == node) {
        return;
    }
    print_avl_tree(node->left);
    printf("%d	%d
", node->data, node->height);
    print_avl_tree(node->right);
}

　　

main.c

#include <stdio.h>

#include "avl.h"

int main() {
    struct AVLNode *root = NULL;
    int ret = avl_insert(&root, 7);
    printf("hello, world
");
    printf("root:address %ld
", (long)root);
    printf("after:%d
", 7);
    print_avl_tree(root);
    avl_insert(&root, 6);
    printf("after:%d
", 6);
    print_avl_tree(root);
    avl_insert(&root, 5);
    printf("after:%d
", 5);
    print_avl_tree(root);
    avl_insert(&root, 7);
    printf("after:%d
", 7);
    print_avl_tree(root);
    avl_insert(&root, 1);
    printf("after:%d
", 1);
    print_avl_tree(root);
    avl_insert(&root, 0);
    printf("after:%d
", 0);
    print_avl_tree(root);
    avl_insert(&root, 9);
    printf("after:%d
", 9);
    print_avl_tree(root);

    ret = avl_find(root, 7);
    printf("find 7 result is %d
", ret);

    ret = avl_find(root, 17);
    printf("find 17 result is %d
", ret);

    ret = avl_del(&root, 7);
    printf("del 7 result is %d
", ret);
    print_avl_tree(root);

    ret = avl_del(&root, 17);
    printf("del 17 result is %d
", ret);
    print_avl_tree(root);



    avl_del_tree(root);
    return 0;
}

　　

#gcc -g main.c avl.c -o main

#./main

hello, world
root:address 27951120
after:7
7 0
after:6
6 0
7 1
after:5
5 0
6 1
7 0
after:7
5 0
6 1
7 0
after:1
1 0
5 1
6 2
7 0
after:0
0 0
1 1
5 0
6 2
7 0
after:9
0 0
1 1
5 0
6 2
7 1
9 0
find 7 result is 1
find 17 result is 2
del 7 result is 0
0 0
1 1
5 0
6 2
9 0
del 17 result is 0
0 0
1 1
5 0
6 2
9 0

应该是正确的。