[数据结构与算法]递归建立二叉树

#include<iostream>
using namespace std;

struct TreeNode {
	int val;
	TreeNode* left;
	TreeNode* right;
	TreeNode() : val(0), left(nullptr), right(nullptr) {}
	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
	TreeNode(int x, TreeNode* left, TreeNode* right) : val(x), left(left), right(right) {}
};

void preOrder(TreeNode* t){
	if (t == NULL)
		return;
	cout << t->val << " ";
	preOrder(t->left);
	preOrder(t->right);
}

void CreateTree(TreeNode*& T, vector<int> v, int &i){
	if (v[i] == -1) {
		T = NULL;
		i++;
	}
	else{
		T = new TreeNode(v[i]);
		if (i == v.size() - 1) return;
		i++;
		CreateTree(T->left, v, i);
		CreateTree(T->right, v, i);
	}
}

int main(){
	TreeNode* root;
	vector<int>v = { 1,2,4,-1,-1,5,-1,-1,3,6,-1,-1,7,-1,-1 };
	int i = 0;
	CreateTree(root, v, i);
	preOrder(root);
	return 0;
}