二叉树遍历

最新推荐文章于 2024-10-21 08:57:50 发布

原创最新推荐文章于 2024-10-21 08:57:50 发布 · 107 阅读

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CC 4.0 BY-SA版权

这篇博客介绍了如何利用栈来实现二叉树的后序、中序和先序遍历。后序遍历中，通过维护一个辅助栈，当节点为空或者已访问时将节点值加入结果。中序遍历时，交替地压入左子节点和从栈中弹出节点。先序遍历则先访问根节点，然后压入右子节点和左子节点。

二叉树后序遍历用栈方法

class  Solution {
public:
	vector<int> postorderTraversal(TreeNode *root) {
		vector<int> result;
		stack<TreeNode*> stackTree;
		TreeNode* node = root;
		TreeNode* pre = nullptr;
		do 
		{
			while (node != nullptr)
			{
				stackTree.push(node);
				node = node->left;
			}
			pre = nullptr;
			while (!stackTree.empty())
			{
				node = stackTree.top();
				stackTree.pop();
				//node为空或者已访问
				if (node->right == pre)
				{
					result.push_back(node->val);
					pre = node;
				}
				else
				{
					stackTree.push(node);
					node = node->right;
					break;
				}
			}
		} while (!stackTree.empty());
			return result;
    }

后序遍历用栈

class Soultion {
public:
	vector<int> inorderTraversal(TreeNode* root) {
		vector<int> result;
		stack<TreeNode*> stackTree;
		TreeNode* node = root;
		while (!stackTree.empty() || node != nullptr) {
			if (node != nullptr) {
				stackTree.push(node);
				node = node->left;
			}
			else {
				node = stackTree.top();
				stackTree.pop();
				result.push_back(node->val);
				node = node->right;
			}
		}
		return result;
	};
};

先序遍历用栈

class Soultion {
public:
	vector<int> preorderTraversal(TreeNode* root) {
		vector<int> result;
        if(root==nullptr){
            return result;
        }
		stack<TreeNode*> stackTree;
		TreeNode* node = root;
		stackTree.push(node);

		while (!stackTree.empty()) {
			node = stackTree.top();
			stackTree.pop();
			result.push_back(node->val);

			if (node->right != nullptr) {
				stackTree.push(node->right);
			}
			if (node->left != nullptr) {
				stackTree.push(node->left);
			}
		}
		return result;
	}		
};