c - 测试或验证红黑树的属性

Question

我将此代码基于 Wikipedia article关于红黑树和CLRS书籍“算法导论”中关于红黑树的部分。如果我运行该程序，它会显示预期的结果。现在我想验证它是好的。如何验证属性而不只是简单地针对某些情况进行测试？我想验证代码是否符合规范。我想我可以编写一个测试用例来构建一个大的红黑树然后释放它，但这仍然只是一个测试而不是一个完整的验证。

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


static char BLACK = 'b';
static char RED = 'r';

struct node {
    int key;
    char color;
    struct node *left, *right, *parent;
};

void insert_repair_tree(struct node* n);
void delete_case1(struct node* n);
void delete_case2(struct node* n);
void delete_case3(struct node* n);
void delete_case4(struct node* n);
void delete_case5(struct node* n);
struct node *LEAF;

struct node *parent(struct node *n) {
    return n->parent; // NULL for root node
}

struct node *grandparent(struct node *n) {
    struct node *p = parent(n);
    if (p == NULL)
        return NULL; // No parent means no grandparent
    return parent(p); // NULL if parent is root
}

struct node *sibling(struct node *n) {
    struct node *p = parent(n);
    if (p == NULL)
        return NULL; // No parent means no sibling
    if (n == p->left)
        return p->right;
    else
        return p->left;
}

struct node *uncle(struct node *n) {
    struct node *p = parent(n);
    struct node *g = grandparent(n);
    if (g == NULL)
        return NULL; // No grandparent means no uncle
    return sibling(p);
}

void rotate_left(struct node *n) {
    struct node *nnew = n->right;
    struct node *p = parent(n);
    assert(nnew != NULL); // since the leaves of a red-black tree are empty, they cannot become internal nodes
    n->right = nnew->left;
    nnew->left = n;
    n->parent = nnew;
    // handle other child/parent pointers
    if (n->right != NULL)
        n->right->parent = n;
    if (p != NULL) // initially n could be the root
    {
        if (n == p->left)
            p->left = nnew;
        else if (n == p->right) // if (...) is excessive
            p->right = nnew;
    }
    nnew->parent = p;
}

void rotate_right(struct node *n) {
    struct node *nnew = n->left;
    struct node *p = parent(n);
    assert(nnew != NULL); // since the leaves of a red-black tree are empty, they cannot become internal nodes
    n->left = nnew->right;
    nnew->right = n;
    n->parent = nnew;
    // handle other child/parent pointers
    if (n->left != NULL)
        n->left->parent = n;
    if (p != NULL) // initially n could be the root
    {
        if (n == p->left)
            p->left = nnew;
        else if (n == p->right) // if (...) is excessive
            p->right = nnew;
    }
    nnew->parent = p;
}

void insert_recurse(struct node* root, struct node* n) {
    // recursively descend the tree until a leaf is found
    if (root != NULL && n->key < root->key) {
        if (root->left != LEAF) {
            insert_recurse(root->left, n);
            return;
        }
        else
            root->left = n;
    } else if (root != NULL) {
        if (root->right != LEAF){
            insert_recurse(root->right, n);
            return;
        }
        else
            root->right = n;
    }

    // insert new node n
    n->parent = root;
    n->left = LEAF;
    n->right = LEAF;
    n->color = RED;
}


void insert_case1(struct node* n)
{
    if (parent(n) == NULL)
        n->color = BLACK;
}

void insert_case2(struct node* n)
{
    return; /* Do nothing since tree is still valid */
}
void insert_case3(struct node* n)
{
    parent(n)->color = BLACK;
    uncle(n)->color = BLACK;
    grandparent(n)->color = RED;
    insert_repair_tree(grandparent(n));
}
void insert_case4step2(struct node* n)
{
    struct node* p = parent(n);
    struct node* g = grandparent(n);

    if (n == p->left)
        rotate_right(g);
    else
        rotate_left(g);
    p->color = BLACK;
    g->color = RED;
}


void insert_case4(struct node* n)
{
    struct node* p = parent(n);
    struct node* g = grandparent(n);

    if (n == g->left->right) {
        rotate_left(p);
        n = n->left;
    } else if (n == g->right->left) {
        rotate_right(p);
        n = n->right;
    }

    insert_case4step2(n);
}



void insert_repair_tree(struct node* n) {
    if (parent(n) == NULL) {
        insert_case1(n);
    } else if (parent(n)->color == BLACK) {
        insert_case2(n);
    } else if (uncle(n)->color == RED) {
        insert_case3(n);
    } else {
        insert_case4(n);
    }
}
struct node *insert(struct node* root, struct node* n) {
    // insert new node into the current tree
    insert_recurse(root, n);

    // repair the tree in case any of the red-black properties have been violated
    insert_repair_tree(n);

    // find the new root to return
    root = n;
    while (parent(root) != NULL)
        root = parent(root);
    return root;
}



void replace_node(struct node* n, struct node* child){
    child->parent = n->parent;
    if (n == n->parent->left)
        n->parent->left = child;
    else
        n->parent->right = child;
}

int is_leaf(struct node* n){
    if(n->right ==NULL && n->left == NULL)
        return 1;
    else return 0;
}

void delete_one_child(struct node* n)
{
    /*
     * Precondition: n has at most one non-leaf child.
     */
    struct node* child = is_leaf(n->right) ? n->left : n->right;

    replace_node(n, child);
    if (n->color == BLACK) {
        if (child->color == RED)
            child->color = BLACK;
        else
            delete_case1(child);
    }
    free(n);
}

void delete_case1(struct node* n)
{
    if (n->parent != NULL)
        delete_case2(n);
}

void delete_case2(struct node* n)
{
    struct node* s = sibling(n);

    if (s->color == RED) {
        n->parent->color = RED;
        s->color = BLACK;
        if (n == n->parent->left)
            rotate_left(n->parent);
        else
            rotate_right(n->parent);
    }
    delete_case3(n);
}

void delete_case3(struct node* n)
{
    struct node* s = sibling(n);

    if ((n->parent->color == BLACK) &&
        (s->color == BLACK) &&
        (s->left->color == BLACK) &&
        (s->right->color == BLACK)) {
        s->color = RED;
        delete_case1(n->parent);
    } else
        delete_case4(n);
}

void delete_case4(struct node* n)
{
    struct node* s = sibling(n);

    if ((n->parent->color == RED) &&
        (s->color == BLACK) &&
        (s->left->color == BLACK) &&
        (s->right->color == BLACK)) {
        s->color = RED;
        n->parent->color = BLACK;
    } else
        delete_case5(n);
}

void delete_case6(struct node* n)
{
    struct node* s = sibling(n);

    s->color = n->parent->color;
    n->parent->color = BLACK;

    if (n == n->parent->left) {
        s->right->color = BLACK;
        rotate_left(n->parent);
    } else {
        s->left->color = BLACK;
        rotate_right(n->parent);
    }
}

void delete_case5(struct node* n)
{
    struct node* s = sibling(n);

    if  (s->color == BLACK) { /* this if statement is trivial,
due to case 2 (even though case 2 changed the sibling to a sibling's child,
the sibling's child can't be red, since no red parent can have a red child). */
/* the following statements just force the red to be on the left of the left of the parent,
   or right of the right, so case six will rotate correctly. */
        if ((n == n->parent->left) &&
            (s->right->color == BLACK) &&
            (s->left->color == RED)) { /* this last test is trivial too due to cases 2-4. */
            s->color = RED;
            s->left->color = BLACK;
            rotate_right(s);
        } else if ((n == n->parent->right) &&
                   (s->left->color == BLACK) &&
                   (s->right->color == RED)) {/* this last test is trivial too due to cases 2-4. */
            s->color = RED;
            s->right->color = BLACK;
            rotate_left(s);
        }
    }
    delete_case6(n);
}

struct node* search(struct node *temp, int val) {
    int diff;
    while (!is_leaf(temp)) {
        diff = val - temp->key;
        if (diff > 0) {
            temp = temp->right;
        } else if (diff < 0) {
            temp = temp->left;
        } else {
            printf("Search Element Found!!\n");
            return temp;
        }
    }
    printf("Given Data Not Found in the tree!!\n");
    return 0;
}
void inorderTree(struct node *root) {
    struct node *temp = root;

    if (temp != NULL) {
        inorderTree(temp->left);

        printf(" %d--%c ", temp->key, temp->color);

        inorderTree(temp->right);

    }
}

void postorderTree(struct node *root) {
    struct node *temp = root;

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

void traversal(struct node *root) {
    if (root != NULL) {
        printf("root is %d-- %c", root->key, root->color);
        printf("\nInorder tree traversal\n");
        inorderTree(root);
        printf("\npostorder tree traversal\n");
        postorderTree(root);
    }
}
int main() {
    printf("Hello!\n");
    struct node *root = NULL;//malloc(sizeof(struct node));
    LEAF = malloc(sizeof(struct node));
    LEAF->color=BLACK;
    LEAF->left=NULL;
    LEAF->right=NULL;
    LEAF->key=0;
    int choice, val, var, fl = 0;
    while (1) {
        setbuf(stdout, 0); // Bugfix for debugging mode on Windows
        printf("\nEnter your choice :1:Add  2:Delete  3:Find  4:Traverse 5: Test  6:Exit\n");
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                setbuf(stdout, 0);
                printf("Enter the integer you want to add : ");
                scanf("%d", &val);
                struct node *z = malloc(sizeof(struct node));
                z->key = val;
                z->left = NULL;
                z->right = NULL;
                z->parent = NULL;
                z->color = RED;
                root = insert(root, z);
                printf("The root is now %d: ", root->key);

                break;
            case 2:
                printf("Enter the integer you want to delete : ");
                scanf("%d", &var);
                delete_one_child(search(root, var));
                break;
            case 3:
                printf("Enter search element \n");
                scanf("%d", &val);
                search(root, val);
                break;
            case 4: 
                traversal(root);
                break;
            case 5: // TODO
                //test();
                break;
            case 6:
                fl = 1;
                break;
            default:
                printf("\nInvalid Choice\n");
        }
        if (fl == 1) { break; }
    }
    return 0;
}

Answer 1

有验证，有证明。也许“完全验证”是指代码正确性的正式证明。但是很多地方验证的意思是:

• 测试数据结构属性的函数
• 在几轮插入和/或删除后重复应用
• 结合代码覆盖率指标确保您的所有代码都得到执行

对于类似 map 的数据结构，我喜欢保留一个简单的并行数据结构，例如树中所有键的哈希表。然后在每轮插入和/或删除之后执行的测试中，您可以验证所有预期的键都在树中，以及树的大小是否正确。当然，这是在红黑不变量成立、树足够平衡、树有序等基本检验之外。

明智的做法是使用带有 key 大小范围参数的随 secret 钥生成器，以避免测试出现偏差。添加随机选择的插入、查找或删除操作，并动态调整比率以将树增长到足够大的大小。运行几个小时，看看能不能达到100%的代码覆盖率； MC/DC 覆盖范围的额外积分。