1043. Is It a Binary Search Tree (25)

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本文介绍了一种使用C++实现的二叉树构建方法，并详细展示了如何通过递归方式完成不同顺序的树节点遍历，包括先序、中序、后序遍历等。此外还提供了释放树内存的方法。

考察建立二叉树，以及树的遍历

#include<iostream>
#include<vector>
#include<queue>

typedef struct Node
{
	int key;
	Node* left;
	Node* right;
	Node(Node* _l = NULL, Node* _r = NULL, int _k = -1)
		:left(_l), right(_r),key(_k){};
}Node;

void InsertTree(Node* &tree, int key)
{
	Node** p = &tree;
	while((*p) != NULL)
	{
		if( key < (*p)->key )
			p = &(*p)->left;
		else p = &(*p)->right;
	}
	(*p) = new Node;
	(*p)->key = key;
}
void ReleaseTree(Node* tree)
{
	std::queue<Node*> q;
	q.push(tree);
	while(!q.empty())
	{
		Node* p = q.front();
		q.pop();
		if(p)
		{
			q.push(p->left);
			q.push(p->right);
			delete p;
		}
	}
}
void TravelRootLR(Node* tree, std::vector<int>& v)
{
	if(tree == NULL) return;
	v.push_back(tree->key);
	TravelRootLR(tree->left, v);
	TravelRootLR(tree->right, v);
}
void TravelRootRL(Node* tree, std::vector<int>& v)
{
	if(tree == NULL) return;
	v.push_back(tree->key);
	TravelRootRL(tree->right, v);
	TravelRootRL(tree->left, v);
}
void TravelLRRoot(Node* tree, std::vector<int>& v)
{
	if(tree == NULL) return;
	TravelLRRoot(tree->left, v);
	TravelLRRoot(tree->right, v);
	v.push_back(tree->key);
}
void TravelRLRoot(Node* tree, std::vector<int>& v)
{
	if(tree == NULL) return;
	TravelRLRoot(tree->right, v);
	TravelRLRoot(tree->left, v);
	v.push_back(tree->key);
}
int main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		std::vector<int> inputVec(n);
		for(int i = 0; i < n; ++i)
			scanf("%d",&inputVec[i]);
		//build tree
		Node* tree = NULL;
		for(int i = 0; i < n; ++i)
			InsertTree(tree, inputVec[i]);
		//get RootLR & RootRL & RLRoot
		std::vector<int> t1, t2, t3;
		TravelRootLR(tree, t1);
		TravelRootRL(tree, t2);
		
		//judge
		//int size = (int)t3.size();
		//if( IsSame(inputVec, t1) || IsSame(inputVec, t2) )
		if(inputVec == t1)
		{
			printf("YES\n");
			TravelLRRoot(tree, t3);
			int size = (int)t3.size();
			for(int i = 0; i < size-1; ++i)
				printf("%d ", t3[i]);
			printf("%d\n", t3[size-1]);
		}
		else if(inputVec == t2)
		{
			printf("YES\n");
			TravelRLRoot(tree, t3);
			int size = (int)t3.size();
			for(int i = 0; i < size-1; ++i)
				printf("%d ", t3[i]);
			printf("%d\n", t3[size-1]);
		}
		else 
		{
			printf("NO\n");
		}
		ReleaseTree(tree);
	}
	return 0;
}