Core becomes a label, video in the interview room, and @mentions in chat

Core is a label, not a tier

Core used to be a fourth difficulty, sitting below Bronze. That mixed two questions: how hard is this problem, and is it one of the textbook implementations everyone should be able to write from memory. Those are now separate.

• Difficulty is Bronze, Silver or Gold. The former Core problems keep the points they were already worth, now under the tier those points belonged to.
• Core is a badge beside the difficulty on the catalog, problem cards, the problem page header and the Learn ladders. It marks the old Core families plus the textbook implementations (binary search, BFS on a grid, edit distance, reversing a linked list, and so on).
• The catalog and your saved lists have a Core toggle that shows only those problems.
• Your profile's difficulty breakdown has a Core line, counted inside its tier.

Video in the mock interview room

Mock interviews now have a video call built into the room. There is no separate meeting link: the booking email, the calendar invite and the upcoming card all say voice and video are in the room.

• Booked and ad-hoc. A booked interview's call lasts its booking window. An interview you start yourself with Start a mock interview gets the call too, for up to 60 minutes from when it first opens; reconnecting does not extend it.
• Check your camera and mic first. A video room opens on a lobby: a camera preview, a live mic level meter, a speaker test, device pickers, camera and mic toggles, and who is already in the room. Test mic records up to five seconds and plays it back so you can hear yourself; nothing leaves your browser. Your picks are remembered. "Join without video" enters the room with a Join call button instead. If the browser has blocked the camera, the lobby says so, tells it apart from "no device" or "in use by another app", and offers a button to ask again.
• Docked or floating. On desktop the call sits at the top of the sidebar; on a phone, above the toolbar. Pop out floats it as a window you drag by its title bar and resize from its corner; Dock puts it back. Resizing the browser no longer drops and rejoins the call. Hide video keeps the call going, and Leave offers Rejoin.
• Call settings open from the gear on the call bar: camera, microphone and speaker pickers, a "Show my own video" switch, and switches for the browser's echo cancellation, noise suppression and auto gain. Turning noise suppression off helps when your voice sounds choppy.

Interview rooms also changed in a few other ways:

• Two seats. Every mock interview room seats two: an interviewer and a candidate. A booked room's seats are both reserved for the two of you, so nobody else can join, even with the code; a room you start yourself still lets the second person in by invite code.
• Private notes. The interviewer's notes stay private after the session unless they switch on sharing for that session. The replay no longer includes notes.
• Cancelling emails the other person, not just an in-app notification: the host hears the slot is open again, the candidate gets a link to book another. Once the room has been opened, the booking can no longer be cancelled.

Open times on profiles

A host's profile now lists their soonest open mock interview times under the stats row, each with its date, time, length and note, plus a "+N more" tile and a Book link to their calendar. On your own profile the same band links to Manage availability.

Profiles also gain social links: GitHub, Twitch, YouTube and LinkedIn, set in Settings → Profile or the Edit Profile form, shown as coloured icons under the bio. The bio itself keeps its line breaks now; before, every newline collapsed into a space.

Chat

• @mentions. Type @ in global chat for an autocomplete of everyone in the loaded history. Mentions render as clickable name chips, a message that names you is tinted, and you get an inbox notification ("X mentioned you in global chat").
• Moderators can now remove messages and time out or ban accounts that abuse chat.

Feed and XP

When someone you follow enters a new rank, the dashboard Activity feed says so ("Ada was promoted to Brute Enforcer"), with the rank insignia linking to /levels.

The "Cleared the room" XP bonus used to say "Everyone in the room solved it". It is awarded when you solve the room's last remaining problem with at least one other person present, and now says so.

The study group results podium shows each person's solve time. Time breaks ties on points, so tied top-three spots no longer look identical with no visible reason for their order.

Faster verdicts

• A time limit used to trigger a second full run to rule out a busy judge. When your code used its whole CPU budget it was computing, not waiting, so that second run only doubled a 15-second wait for the same answer. It is now skipped in that case.
• A failed hidden case used to need a second run to show its output. Small outputs now come back with the first run, so the failing case appears right away; only very large outputs still need the extra run.
• The starter code and test cases now load together instead of one after the other.

Daily challenge

The daily challenge now avoids any problem picked in the previous 365 days, up from 30. If every eligible problem has been used within the year, the one picked longest ago comes around again, so there is never a day without a challenge.

BlazerBot

BlazerBot led with a question on every turn, which got tiring when you just wanted an answer. It now answers the question you asked. It asks a coaching question only when you are stuck or share wrong code and have not asked for the answer, and "just tell me" or "no hints" switches it to giving full answers for the rest of the conversation. Asked whether an approach is right, it says right or wrong and names the one case that breaks it.

New logo

The Algo Blazer mark is redrawn: a ring split into two arcs like a pair of brackets, around a flame whose core is filled with the theme accent. It appears beside the wordmark, as the tab icon, and in the rank insignia.

Smaller fixes

• A problem's examples appeared twice when its statement had its own Examples section: once in the statement, once in the sample panel below. They now appear once.
• If you had a lot of accepted submissions, your profile could miss a handful of solved problems, and it counted problems that had been pulled from the site. It now counts exactly the problems listed on /learn/all.
• After confirming your email from the signup link, the header kept showing Log in and Sign up until you reloaded. It now shows you signed in. The signup page also reminds you to check your spam folder for that email.
• Each /changelog entry is now titled by its one-line summary, with the date underneath.

Problem reports

Thanks to everyone who used Report on a problem. Fixes from this round:

• Kth Node in Subtree Preorder: Example 1 now draws the tree.
• Most Negative Balance Names: Examples 2 and 3 walk through the records one at a time with the balances after each.
• Minimum Parallel Completion Time: the statement says the answer is when the last worker finishes and what idle workers do; it is now Silver.
• Missing Arithmetic Term: new tests catch a solution that assumed the smaller gap is the step.
• Is Toeplitz Matrix: a sentence that gave away the solution is gone.
• Circular One-Pair Maximum Sum left the 1D DP ladder, where it did not fit.