Given a binary tree, return the inorder traversal of its nodes‘ values.
For example:
Given binary tree [1,null,2,3]
,
1 2 / 3
return [1,3,2]
.
Note: Recursive solution is trivial, could you do it iteratively?
我的AC代码,递归写法比较简单,所以试试迭代:
class Solution { public: vector<int> inorderTraversal(TreeNode* root) { vector<int> nums; stack<TreeNode *> stackNode; while(root) { stackNode.push(root); if (root->left != NULL) { root = root->left; continue; } nums.push_back(root->val); stackNode.pop(); if (root->right != NULL) { root = root->right; continue; } TreeNode * node = root; if (!stackNode.empty()) { root = stackNode.top(); root->left = NULL; stackNode.pop(); } if (node == root) break; } return nums; } };
利用递归栈的思路,自己维护一个栈,时间复杂度应该是O(n),空间复杂度O(n)。
看看AC后的详细细节:
运行时间是3ms。
不过我也写了一个递归版的:
class Solution { public: void helper(TreeNode* root, vector<int> & nums) { if (root) { helper(root->left, nums); nums.push_back(root->val); helper(root->right, nums); } } vector<int> inorderTraversal(TreeNode* root) { vector<int> nums; helper(root, nums); return nums; } };
这个运行结果感觉差不多:
完整的迭代算法:
#include <iostream> #include <vector> #include <stack> using namespace std; class Tree { public: int val; Tree * left; Tree * right; Tree() : val(), left(NULL), right(NULL) {} void CreateTree(Tree * &root); Tree* insert(Tree * root, int x); void buildTree(Tree* root, vector<int> nums); void inorderTraversal(Tree * root); void iterative_inorderTraversal(Tree * root); }; void Tree::CreateTree(Tree * &root) { int val; cin >> val; if (val == -1) root = NULL; else { root = new Tree; root->val = val; CreateTree(root->left); CreateTree(root->right); } } Tree* Tree::insert(Tree * root, int x) { Tree * node = new Tree; node->val = x; if (root == NULL) { root = node; return root; } else if (root->left == NULL) { root->left = node; return root; } else if (root->right == NULL) { root->right = node; return root; } else node->left = root; return node; } void Tree::buildTree(Tree* root, vector<int> nums) { for (auto n : nums) root = insert(root, n); } void Tree::inorderTraversal(Tree * root) { if (root != NULL) { inorderTraversal(root->left); cout << root->val << ‘ ‘; inorderTraversal(root->right); } } void Tree::iterative_inorderTraversal(Tree * root) { stack<Tree *> stackNode; while(root) { stackNode.push(root); if (root->left != NULL) { root = root->left; continue; } cout << root->val << ‘ ‘; stackNode.pop(); if (root->right != NULL) { root = root->right; continue; } Tree * node = root; if (!stackNode.empty()) { root = stackNode.top(); root->left = NULL; stackNode.pop(); } if (node == root) break; } } int main() { //vector<int> nums{ 1,2,3 }; Tree * root = NULL; root->CreateTree(root); //root->buildTree(root, nums); root->inorderTraversal(root); cout << endl; root->iterative_inorderTraversal(root); return 0; }
原文地址:https://www.cnblogs.com/darkchii/p/8576029.html
时间: 2024-10-15 12:33:50