[LeetCode]Binary Tree Preorder Traversal

最新推荐文章于 2022-07-19 12:03:10 发布

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本文介绍了一种使用栈实现二叉树前序遍历的方法。通过迭代而非递归的方式，该算法有效地遍历了二叉树并返回节点值的序列。此方法适用于需要节省调用栈空间的应用场景。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> preorderTraversal(TreeNode *root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        vector<int> result;
        stack<TreeNode*> nodeStack;
        TreeNode* curNode = root;
        while(curNode || !nodeStack.empty())
        {
            if(curNode) result.push_back(curNode->val);
            //...process left recursive call
            while(curNode)
            {
                nodeStack.push(curNode);
                curNode = curNode->left;
                if(curNode) result.push_back(curNode->val);
            }
            //..process the rest after left recursive call
            if(!nodeStack.empty())
            {
                curNode = nodeStack.top();
                nodeStack.pop();
                curNode = curNode->right;
            }
        }
        
        return result;
    }
};