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();}
}