Question

我正在写一个B树的symulator。我在这里阅读stackoverflow，最好的方法是使用队列进行级别顺序遍历。但我不知道该怎么做。我从geeksforgeeks开始用c ++实现。也许有人知道如何重建inorder遍历（下面的代码）到级别顺序遍历。

类和构造函数：

sonar-runner

顺序遍历：

class BTreeNode
{
    int *keys;  // An array of keys
    int t;      // Minimum degree (defines the range for number of keys)
    BTreeNode **C; // An array of child pointers
    int n;     // Current number of keys
    int j;
    bool leaf; // Is true when node is leaf. Otherwise false
public:
    BTreeNode(int _t, bool _leaf);   // Constructor

    // A utility function to insert a new key in the subtree rooted with
    // this node. The assumption is, the node must be non-full when this
    // function is called
    void insertNonFull(int k);

    // A utility function to split the child y of this node. i is index of y in
    // child array C[].  The Child y must be full when this function is called
    void splitChild(int i, BTreeNode *y);

    // A function to traverse all nodes in a subtree rooted with this node
    void traverse();



// A function to search a key in subtree rooted with this node.
    BTreeNode *search(int k);   // returns NULL if k is not present.

// Make BTree friend of this so that we can access private members of this
// class in BTree functions
friend class BTree;
};

// A BTree
class BTree
{
    BTreeNode *root; // Pointer to root node
    int t;  // Minimum degree
public:
    // Constructor (Initializes tree as empty)
    BTree(int _t)
    {  root = NULL;  t = _t; }

    // function to traverse the tree
    void traverse()
    {  if (root != NULL) 
    cout << "root";
    root->traverse(); }


    // function to search a key in this tree
    BTreeNode* search(int k)
    {  return (root == NULL)? NULL : root->search(k); }

    // The main function that inserts a new key in this B-Tree
    void insert(int k);
};

Answer 1

在这里，您可以看到Depth-First-Search算法（wiki）的递归实现对于逐级遍历，您可能需要广度优先搜索（wiki）。

为实现这一目标，我们将执行两个步骤第一步：编写无递归DFS：

void BTreeNode::traverse()
{
    std::stack<BTreeNode*> stack;
    stack.push(this);
    while (!stack.empty())
    {
        BTreeNode* current = stack.top();
        stack.pop();
        int i;
        for (i = 0; i < n; i++)
        {
            if (leaf == false)
                stack.push(current->C[i]); 
            cout << " " << current->keys[i];
        }
        if (leaf == false)
            stack.push(current->C[i]);
    }
}

第二步：使用队列而不是堆栈：

void BTreeNode::traverse()
{
    std::queue<BTreeNode*> queue;
    queue.push(this);
    while (!stack.empty())
    {
        BTreeNode* current = queue.front();
        queue.pop();
        int i;
        for (i = 0; i < n; i++)
        {
            if (leaf == false)
                stack.push(current->C[i]); 
            cout << " " << current->keys[i];
        }
        if (leaf == false)
            stack.push(current->C[i]);
    }
}

所以，它已经完成了！

B树的级别顺序遍历

1 个答案: