LeetCode 94. Binary Tree Inorder Traversal

最新推荐文章于 2022-06-30 15:29:15 发布

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本文介绍了一种实现二叉树中序遍历的方法，包括递归与迭代两种方式。通过栈结构来辅助实现非递归的中序遍历，并提供了一种迭代器模式的应用思路。

Given a binary tree, return the inorder traversal of its nodes' values.

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

return [1,3,2].

 vector<int> inorderTraversal(TreeNode* root) {
    if(!root) return {};
    vector<int> res;
    stack<TreeNode*> nodes;
    TreeNode* pCurrent = root;
    while(!nodes.empty() || pCurrent) {
        if(pCurrent) {
            nodes.push(pCurrent);
            pCurrent = pCurrent->left;
        } else {
            TreeNode* tmp = nodes.top();
            nodes.pop();
            res.push_back(tmp->val);
            pCurrent = tmp->right;
        }
    }
    return res;
}

Or, it might ask for iterator

stack<TreeNode*> nodes;

BinaryTree (TreeNode* root) {
  if(root->left) {
    nodes.push_back(root);
    root = root->left;
  }
}

bool hasNext() {
  return !nodes.empty();
}

int getNext() {
  if(hasNext()) {
    TreeNode* tmp = nodes.top();
    nodes.pop();
    if(tmp->right) {
      TreeNode* node = tmp->right;
      while(node) {
        nodes.push_back(node);
        node = node->left;
      }
    }
    return tmp->val;
  }
  return -1;
}