二叉树非递归遍历(C++版本)

来源：互联网发布：ifconfig 修改mac 编辑：程序博客网时间：2024/05/28 09:31

二叉树非递归遍历有三种方式：前序遍历、中序遍历、后续遍历

前序遍历

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

中序遍历

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

后续遍历

class Solution {public:    vector<int> postorderTraversal(TreeNode* root) {        vector<int> res;        stack<TreeNode *> s;        TreeNode * lastNode = NULL, *topNode = NULL;        while (root || !s.empty()){            while (root){                s.push(root);                root = root->left;            }            topNode = s.top();            // topNode->right != lastNode 表示lastNode 这个节点下面的节点已经遍历过，没有必要再遍历了...            if (topNode->right != NULL && topNode->right != lastNode){                root = topNode->right;            }            else{                res.push_back(topNode->val);                lastNode = topNode;                s.pop();            }        }        return res;    }};

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