Ch4.4: array to Balanced tree and print each level-优快云博客

本文介绍如何将一个有序数组转换为平衡二叉搜索树，并通过广度优先搜索（BFS）逐层输出各节点形成D维链表。涉及知识点包括链表、向量、递归、成员函数作用域、引用调用、类和模板等。源代码示例展示了树的构造过程以及BFS遍历的具体实现。

Q: an ordered array is given, need to convert into a balanced binary tree and then BFSly print each level as a D-dimentional linked list

Need to understand list, vector, BFS, recursion, scope of member function, call-by-reference, class, template.

The main method is the linked list form processing.

1: push the given head into the list, then push it into a vector.

2. if the vector is not empty, push all the left/right children of the head into a temporary list, after BFS this level, push the temp list into the previous vector as output.

Here is the source code and output.

// Ch4.4: Given a binary search tree, design an algorithm which creates a linked list of all the nodes at each depth (i.e., if you have a tree with depth D, you’ll have D linked lists).

// based on Hawstein's solution
// and zyli's github

#include 
#include 
#include 

using namespace std;

class BinNode{
public:
    int key;
    BinNode *parent, *lChild, *rChild;
	BinNode(){}
	BinNode(int t): key(t), parent(NULL), lChild(NULL), rChild(NULL){}
};

class BTree{
private:
	BinNode *m_root;
public:
	BTree(): m_root(NULL){}
	BTree(BinNode *t): m_root(t){}

	BinNode* getRoot() const{return m_root;}
	
	BinNode* balanceTree(BinNode* pnode, BinNode *parent, int *arr, int low, int high){
		if(low>high || arr == NULL)
			return NULL;
		int mid = (low+high)>>1;
		pnode = new BinNode(arr[mid]);
		pnode->parent = parent;
		pnode->lChild = balanceTree(pnode->lChild, pnode, arr, low, mid-1);
		pnode->rChild = balanceTree(pnode->rChild, pnode, arr, mid+1, high);

		return pnode;
	}

	void PrintPre(BinNode *pnode)
	{
		if(pnode == NULL)
			return;
 
		cout << pnode->key << " ";
		PrintPre(pnode->lChild);
		PrintPre(pnode->rChild);		
	}

    vector> BFSlist(BinNode *head){
        vector> res;
    	int level = 0;
    	list li;
    	li.push_back(head);
    	res.push_back(li);
    	while(!res[level].empty()){
    		list l;
    		list::iterator it;
    		for(it=res[level].begin(); it!=res[level].end(); ++it){
    			BinNode *n = *it;
    			if(n->lChild) l.push_back(n->lChild);
    			if(n->rChild) l.push_back(n->rChild);
    		}
    		++level;
    		res.push_back(l);
    	}
    	return res;
    }

    void print(vector > res){
        vector >::iterator vit;
        for(vit=res.begin(); vit!=res.end(); ++vit){
            list li = *vit;
            list::iterator lit;
            for(lit=li.begin(); lit!=li.end(); ++lit){
                BinNode *n = *lit;
                cout<key<<" ";
            }
            cout<balanceTree(bt->getRoot(), NULL, arr, low, high);
    bt = new BTree(proot);
    bt->PrintPre(bt->getRoot());
    cout << "\nD-dimesion linked list showoff-------\n";
    vector> jerry = bt->BFSlist(proot);
    bt->print(jerry);
}

/////////////////////////////////////////////////////////////////////////////
/*output:
Executing the program....
$demo 
Balanced tree in array format
10 2 1 5 7 15 13 21 22 
D-dimesion linked list showoff-------
10 
2 15 
1 5 13 21 
7 22 
*/