【leetcode刷題】棧的方式先序二叉樹

問題：

5.1.1 Binary Tree Preorder Traversal

描述

Given a binary tree, return the preorder traversal of its nodes’ values.

For example: Given binary tree {1,#,2,3},

Note: Recursive solution is trivial, could you do it iteratively?

分析：用棧或者 Morris 遍歷。 

實現：增添了一個makeTree()方法，生成需要的二叉樹。

#include<vector>
#include<iostream>
#include<stdlib.h>
#include<stack>
#include<vector>
#include<cmath>
// #include<iterator>

using namespace std;
static int count = 0;

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

//棧的方式實現前序遍歷
vector<int> preorderTraversal(TreeNode* root){
	vector<int> result;
	stack<TreeNode *> stackTree;
	TreeNode* p = root;

	if(p != nullptr){
		stackTree.push(root);
	}

	while(!stackTree.empty()){
		p = stackTree.top();
		stackTree.pop();

		result.push_back(p->val);
		if(p->right != nullptr) stackTree.push(p->right);
		if(p->left != nullptr) stackTree.push(p->left);
	}
	return result;
}

int treeDeep(int n){
	int i = 0;
	if( n == 1){
		return 2;
	}else{
		while(i < 20){
			if(n > pow(2,i)-2 && n <= pow(2,i+1)-2){
				return (i+1);	
			}
			i++;
		}	
	}
	
	return 0;
}
void printTree(TreeNode *root){
	cout<<root->val<<" ";
	if(root->left != nullptr){
		printTree(root->left);
	}
	if(root->right != nullptr){
		printTree(root->right);
	}
}

TreeNode* selectTree(TreeNode *root,int k){
	cout<<root->val<<",";
	if(root->left != nullptr){
		count++;
		cout<<"left:"<<count<<";"<<endl;
		cout<<root->left->val<<",";
		if(count == k){
			return root->left;
		}
	}
	if(root->right != nullptr){
		count++;
		cout<<"right:"<<count<<";"<<endl;

		cout<<root->right->val<<",";
		if(count == k){
			return root->right;
		}
	}
	selectTree(root->left,k - count);
	selectTree(root->right,k - count);
}

void makeTree(TreeNode* root,int k){
	TreeNode *tmpTree = new TreeNode(1);
	sranddev();
	tmpTree->val = rand()%100;

	if(count < k && root->left == nullptr){
		root->left = tmpTree;
		count++;
	}else if(count < k && root->right == nullptr){
		root->right = tmpTree;
		count++;
	}

	if(count < k){
		makeTree(root->left,k);
		makeTree(root->right,k);
	}
}
int main(){
	TreeNode *root = new TreeNode(10);

	int size;
	size = 10;

	TreeNode *root1,*root2;
	root1 = root2;

	// for(int i = 1; i < 10;++i){
	// 	int deep = treeDeep(i);
	// 	cout<<"i="<<i<<"deep="<<deep<<endl;

	// 	TreeNode *tmpTree = new TreeNode(1);
	// 	sranddev();
	// 	tmpTree->val = rand()%100;

	// 	if(i % 2 == 1){
	// 		root1 = root;
	// 		for(int j = 0; j < deep-1 &&(!root1);j++){
	// 			root1 = root1->left;
	// 		}
	// 		root1->left = tmpTree;
	// 	}else{
	// 		root2 = root;

	// 		for(int j = 0; j < deep-1 && (!root2);j++){
	// 			root2 = root2->right;
	// 		}
	// 		root2->right = tmpTree; 
	// 	}
	// }
	makeTree(root,10);
	printTree(root);
	cout<<endl;
	// selectTree(root,2);
	// cout<<endl;

	vector<int> res;
	res = preorderTraversal(root);

	for(vector<int>::iterator it = res.begin(); it != res.end();it++){
		cout<<*it<<" ";
	}
	cout<<endl;
}