1020. Tree Traversals 解析

后序与中序构建二叉树并层序遍历

最新推荐文章于 2025-06-24 14:10:30 发布

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本文介绍了一种利用给定的后序遍历和中序遍历序列构建二叉树的方法，并实现了对该二叉树进行层序遍历的功能。通过C++代码实现，详细展示了如何定位根节点、递归构建左右子树的过程。

我是直接由后序和中序建树然后层序遍历。

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

using namespace std;

vector <int> post;
vector <int> in;

int N, Count = 0;

struct Node {
	int data;
	Node * L;
	Node * R;
};

typedef Node * Tree;


Tree BuildTree(int inst,int ined, int postst ,int posted) {
	Tree t = new Node;
#ifdef _DEBUG
	cout << "in: " << inst << " " << ined ;
	cout << " Post: " << postst << " " << posted << endl;
#endif
	if (postst <= posted) {
		t->data = post[posted];
#ifdef _DEBUG
		cout << post[posted] << endl;
#endif
		int L = 0; int R = 0; int tempI = 0;
		bool isFind = false, isLR = false;
		for (int i = inst; i <= ined; i++) {
			if (in[i] == post[posted]) {
				isFind = true;
				isLR = true;
				tempI = i;
			}

			if (!isLR) L++;
			else R++;
		}
		R--;
#ifdef _DEBUG
		cout << "L " << L << " R " << R << endl;
#endif
		if (isFind) {
			t->L = BuildTree(inst, tempI - 1, postst, postst + L - 1);
			t->R = BuildTree(tempI + 1, ined, postst + L, posted - 1);
		}
		else return NULL;
	}
	else t = NULL;

	return t;

}

void PreOrder(Tree T) {
	if(T){
		cout << T->data << " ";
		PreOrder(T->L);
		PreOrder(T->R);
	}
}

vector <int> s;
void LevelOrder(Tree T) {
	queue <Tree> q;
	Tree temp;
	if (T) {
		q.push(T);
		while (!q.empty()) {
			temp = q.front();
//			cout << q.size() << endl;
			s.push_back(temp->data);
			q.pop();
			if (temp->L) q.push(temp->L);
			if (temp->R) q.push(temp->R);
		}
	}
}

int main() {
	int  temp;
	cin >> N;
	for (int i = 0; i < N; i++) {
		cin >> temp;
		post.push_back(temp);
	}
	for (int i = 0; i < N; i++) {
		cin >> temp;
		in.push_back(temp);
	}
	Tree T = BuildTree(0,N-1,0,N-1);
	//PreOrder(T);
	LevelOrder(T);
	
	for (int i = 0; i < s.size() - 1; i++) {
		cout << s[i] << " ";
	}
	cout << s[s.size()- 1] << endl;

	system("pause");

	return 0;
}