二叉树的中序遍历- 二叉树基本-栈

 

 

 前序遍历非递归实现​​：

void preorderIterative(TreeNode* root) {
    if (root == nullptr) return;
    stack<TreeNode*> s;
    s.push(root);
    while (!s.empty()) {
        TreeNode* node = s.top();
        s.pop();
        cout << node->val << " ";
        if (node->right) s.push(node->right);
        if (node->left) s.push(node->left);
    }
}

　　

中序遍历非递归实现​​：

 

void inorderIterative(TreeNode* root) {
    stack<TreeNode*> s;
    TreeNode* curr = root;
    while (curr != nullptr || !s.empty()) {
        while (curr != nullptr) {
            s.push(curr);
            curr = curr->left;
        }
        curr = s.top();
        s.pop();
        cout << curr->val << " ";
        curr = curr->right;
    }
}

　　

 后序遍历非递归实现​​：

void postorderIterative(TreeNode* root) {
    if (root == nullptr) return;
    stack<TreeNode*> s1, s2;
    s1.push(root);
    while (!s1.empty()) {
        TreeNode* node = s1.top();
        s1.pop();
        s2.push(node);
        if (node->left) s1.push(node->left);
        if (node->right) s1.push(node->right);
    }
    while (!s2.empty()) {
        cout << s2.top()->val << " ";
        s2.pop();
    }
}