94. Binary Tree Inorder Traversal

最新推荐文章于 2021-09-23 07:24:48 发布

原创最新推荐文章于 2021-09-23 07:24:48 发布 · 76 阅读

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本文详细介绍了二叉树的中序遍历算法，包括递归和迭代两种实现方式。递归方法简洁直观，而迭代方法使用栈来避免递归调用，适合于资源受限的环境。

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中序遍历：

# recursively
def inorderTraversal1(self, root):
    res = []
    self.helper(root, res)
    return res
    
def helper(self, root, res):
    if root:
        self.helper(root.left, res)
        res.append(root.val)
        self.helper(root.right, res)
 
# iteratively       
def inorderTraversal(self, root):
    res, stack = [], []
    while True:
        while root:
            stack.append(root)
            root = root.left
        if not stack:
            return res
        node = stack.pop()
        res.append(node.val)
        root = node.right

Iterative solution using stack

class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> nodes;
        stack<TreeNode*> todo;
        while (root || !todo.empty()) {
            while (root) {
                todo.push(root);
                root = root -> left;
            }
            root = todo.top();
            todo.pop();
            nodes.push_back(root -> val);
            root = root -> right;
        }
        return nodes;
    }
};
Recursive solution

class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> nodes;
        inorder(root, nodes);
        return nodes;
    }
private:
    void inorder(TreeNode* root, vector<int>& nodes) {
        if (!root) {
            return;
        }
        inorder(root -> left, nodes);
        nodes.push_back(root -> val);
        inorder(root -> right, nodes);
    }
};