Diagram kinds

Each kind of question gets the diagram that fits it. Tap Next or swipe the diagram. Objects: see the DI card.

Sequence

How does JWT authentication work end to end?

Also for: Login, OAuth, cache-aside, retries, tool calling, sagas

Angularbrowser

.NET APIApp Service

SQLUsers table

POST /auth/login email + password

1/9The login form posts email and password over HTTPS.

Timeline

switchMap vs mergeMap: which one for a search box?

Also for: RxJS, async/await, threads, event loop, change detection

operator: switchMap

you type

debounceTime(300)

switchMap → HTTP

list on screen

0 ms

1/7Four streams, time runs right. Watch which search reaches the screen.

Pipeline

What is middleware and why does order matter?

Also for: Middleware, filters, interceptors, CI/CD, RAG pipeline

Angular

GET /loans/42

User: (nobody yet)

UseExceptionHandlerwraps everything below

UseAuthenticationtoken → HttpContext.User

UseAuthorizationchecks [Authorize]

LoansController actionMapControllers routes here

1/8Each app.Use…() line in Program.cs adds one middleware, and a request passes them in the order you wrote them. (UseRouting and UseCors sit here too; left out to keep it short.)

Architecture map

Walk me through a request across your Azure system.

Also for: HLD, Azure, microservices, your project walkthrough

BrowserAngular app

Front DoorTLS, WAF, routing

App Service.NET API

Azure SQLApplications table

Application Insightsone operation id across every hop

Service Bus queuecredit-checks

Azure Functionqueue trigger

Dead-letter queueafter 10 failed tries

Credit bureauexternal, slow, flaky

1/9The whole system. Follow one loan application through it. On a phone the view moves to each part; on a laptop you see it all.

Tables

INNER vs LEFT JOIN: what comes back, and what goes wrong?

Also for: Joins, GROUP BY / HAVING, window functions, duplicates, Nth highest

SELECT c.Name, l.Amount
FROM Customers c
JOIN Loans l ON l.CustId = c.Id

Customers c
Id	Name
1	Asha
2	Ravi
3	Meera

Loans l
Id	CustId	Amount
101	1	500000
102	1	200000
103	2	800000

1/7Two tables. A loan points to its customer through CustId. Which customers come back?

Cells

Two Sum: find two numbers that add up to a target.

Also for: Arrays, two pointers, sliding window, linked lists, trees

nums = [3, 8, 11, 4, 6], target = 10

112

seen: value → index

empty

int[] TwoSum(int[] nums, int target) {  var seen = new Dictionary<int, int>();  for (int i = 0; i < nums.Length; i++) {    int need = target - nums[i];    if (seen.TryGetValue(need, out int j))      return [j, i];    seen[nums[i]] = i;  }  return [];}

1/7Find two numbers that add up to 10. Checking every pair is O(n²). One pass with a dictionary is O(n).

Tables: fixed source, changing rows

WHERE vs HAVING with GROUP BY: which rows count, and when?

Also for: GROUP BY / HAVING, aggregates, UPDATE or INSERT between two runs, EF change tracking: the source stays on screen while the result builds

SELECT Contract, SUM(Amount) AS Owed
FROM Payments
WHERE Paid = 'no'
GROUP BY Contract
HAVING COUNT(*) >= 2

Payments p
Id	Contract	Amount	Paid
1	BMW-1001	450	yes
2	BMW-1002	600	no
3	BMW-1001	450	yes
4	BMW-1003	300	yes
5	BMW-1002	600	no

1/6One row per monthly payment. Collections asks: which contracts missed two or more?

Tree

Clustered index: how does SQL Server find one loan without reading the table?

Also for: Index B-trees and query plans (SQL), BST search and validation, recursion and merge-sort trees (DSA), component and file trees (Angular)

Root page1–400 · 401–800

1–400page 2

401–800page 3

1–200rows

201–400rows

401–600rows

601–800rows

1/5A clustered index on LoanId stores the Loans table itself as this tree, sorted by LoanId.