Leedcode6-binary-tree-preorder-traversal

#include<iostream> #include<vector> #include<stack> using namespace std; // Definition for binary tree 先序遍历 根左右 struct TreeNode {int val;TreeNode *left;TreeNode *right;TreeNode(int x) : val(x), left(NULL), right(NULL) {} }; #if 0 class Solution { //me ok public:vector<int> v;vector<int> preorderTraversal(TreeNode *root) {if (root == NULL)return v;v.push_back((*root).val);if((*root).left!=NULL)preorderTraversal((*root).left);if((*root).right!=NULL)preorderTraversal((*root).right);return v;} }; #endif #if 0 class Solution { public:vector<int>res;vector<int> preorderTraversal(TreeNode *root) {if (root == NULL)return res;res.push_back(root->val);if (root->left != NULL)preorderTraversal(root->left);if (root->right != NULL)preorderTraversal(root->right);return res;} }; #endif#if 0 //我非迭代 错误 class Solution { public:vector<int> v;vector<int> preorderTraversal(TreeNode *root) {stack<TreeNode*> s;s.push(root);while (!s.empty()) {TreeNode *node = s.top();s.pop();if (node != NULL)v.push_back(node->val);if (node->left != NULL)s.push(node->left);if (node->right != NULL)s.push(node->right);}} }; #endif#if 1 //我非迭代 class Solution { public:vector<int> v;stack<TreeNode*> s;vector<int> preorderTraversal(TreeNode *root) {if (root ==NULL) {return v;}s.push(root);while (!s.empty()) {TreeNode *node = s.top();s.pop();v.push_back(node->val);if (node->right != NULL)s.push(node->right);if (node->left != NULL)s.push(node->left);}return v;} }; #endif

 

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