二叉树的遍历

最新推荐文章于 2024-08-17 19:33:32 发布

原创最新推荐文章于 2024-08-17 19:33:32 发布 · 164 阅读

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先序遍历（前序遍历）：

遍历顺序规则为根->左->右

递归：

void preOrder(TreeNode* root) {
    if (!root) {
        return;
    }
    cout << root->val;
    preOrder(root->left);
    preOrder(root->right);
}

非递归：

void preorder_traversal_iteratively(TreeNode* root)
{
    if (root == 0)
        return;
    stack<TreeNode*> s;
    s.push(root);
    cout << root->val << ' '; // visit root
    TreeNode* last_pop = root;
    while (!s.empty())
    {
        TreeNode* top = s.top();
        if (top->left != 0 && top->left != last_pop && top->right != last_pop) // push_left
        {
            s.push(top->left);
            cout << top->left->val << ' '; // visit top->left
        }
        else if (top->right != 0 && top->right != last_pop && (top->left == 0 || top->left == last_pop)) // push_right
        {
            s.push(top->right);
            cout << top->right->val << ' '; // visit top->right
        }
        else // pop
        {
            s.pop();
            last_pop = top;
        }
    }
}

中序遍历：

遍历顺序规则为左->根->右

递归：

void inOrder(TreeNode* root) {
    if (!root) {
        return;
    }
    inOrder(root->left);
    cout << root->val;
    inOrder(root->right);
}

非递归：

void inorder_traversal_iteratively(TreeNode* root)
{
    if (root == 0)
        return;
    stack<TreeNode*> s;
    s.push(root);
    TreeNode* last_pop = root;
    while (!s.empty())
    {
        TreeNode* top = s.top();
        if (top->left != 0 && top->left != last_pop && top->right != last_pop) // push_left
        {
            s.push(top->left);
        }
        else if (top->right != 0 && top->right != last_pop && (top->left == 0 || top->left == last_pop)) // push_right
        {
            s.push(top->right);
            cout << top->val << ' '; // visit top
        }
        else // pop
        {
            s.pop();
            last_pop = top;
            if (top->right == 0)
                cout << top->val << ' '; // visit top
        }
    }
}

后序遍历：

遍历顺序规则为左->右->根

递归：

void postOrder(TreeNode* root) {
    if (!root) {
        return;
    }
    postOrder(root->left);
    postOrder(root->right);
    cout << root->val;
}

非递归：

void postorder_traversal_iteratively(TreeNode* root)
{
    if (root == 0)
        return;
    stack<TreeNode*> s;
    s.push(root);   
    TreeNode* last_pop = root;
    while (!s.empty())
    {       
        TreeNode* top = s.top();
        if (top->left != 0 && top->left != last_pop && top->right != last_pop) // push_left
        {
            s.push(top->left);
        }
        else if (top->right != 0 && top->right != last_pop && (top->left == 0 || top->left == last_pop)) // push_right
        {
            s.push(top->right);
        }
        else // pop
        {
            s.pop();
            last_pop = top;
            cout << top->val << ' '; // visit top
        }
    }
}