二叉树的非递归遍历c++

以下是二叉树的非递归遍历C语言代码：

1. 非递归先序遍历

void preorderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    stack<TreeNode*> s;
    s.push(root);
    while (!s.empty()) {
        TreeNode* node = s.top();
        s.pop();
        printf("%d ", node->val);
        if (node->right) {
            s.push(node->right);
        }
        if (node->left) {
            s.push(node->left);
        }
    }
}

2. 非递归中序遍历

void inorderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    stack<TreeNode*> s;
    TreeNode* node = root;
    while (!s.empty() || node != NULL) {
        if (node != NULL) {
            s.push(node);
            node = node->left;
        } else {
            node = s.top();
            s.pop();
            printf("%d ", node->val);
            node = node->right;
        }
    }
}

3. 非递归后序遍历

void postorderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    stack<TreeNode*> s;
    s.push(root);
    TreeNode* pre = NULL;
    while (!s.empty()) {
        TreeNode* node = s.top();
        if ((node->left == NULL && node->right == NULL) || (pre != NULL && (pre == node->left || pre == node->right))) {
            printf("%d ", node->val);
            s.pop();
            pre = node;
        } else {
            if (node->right != NULL) {
                s.push(node->right);
            }
            if (node->left != NULL) {
                s.push(node->left);
            }
        }
    }
}