2020-10-12由完全二叉树的层序遍历求先序、中序、后序

 由完全二叉树的层序遍历求先序、中序、后序，其中-1表示该节点处为NULL

#include<bits/stdc++.h>
using namespace std;

struct node
{
	int val;
	node* left;
	node* right;
	node(int x) : val(x), left(NULL), right(NULL) {}
};

vector<int> before;
vector<int> mid;
vector<int> back;

void dfs(node* root) {
	if (!root) {
		return;
	}
    if(root->val != -1)
	    before.push_back(root->val);
	dfs(root->left);
    if(root->val != -1)
	    mid.push_back(root->val);
	dfs(root->right);
    if(root->val != -1)
	    back.push_back(root->val);
}
vector<vector<int>> binaryTreeScan(int* input, int inputLen) {
	vector<vector<int>> ans;
	if (inputLen <= 0) return ans;
	node* root = new node(input[0]);
	int n = 1;
	int m = 0;
	queue<node*> q;
	q.push(root);
	while (n < inputLen) {
		int cur_len = pow(2, m);
		m++;
		while (cur_len-- && n < inputLen) {
			q.front()->left = new node(input[n++]);
			q.push(q.front()->left);
			q.front()->right = new node(input[n++]);
            q.push(q.front()->right);
			q.pop();
		}
	}
	dfs(root);
	ans.push_back(before);
	ans.push_back(mid);
	ans.push_back(back);
	return ans;
}

void print(vector<vector<int>> arr) {
	for (auto vec : arr) {
		for (auto i : vec) {
			cout << i << " ";
		}
		cout << endl;
	}
}
int main() {
	// int input[] = { 1, 7, 2, 6, -1, 4, 8 };
    int input[] = {1, -1, 2, -1, -1, -1, 3};
	vector<vector<int>> ans = binaryTreeScan(input, 7);
	print(ans);
	return 0;
}