Level 5 · Interview mastery
Free Timed practice lessons
10 lessons, about 3 hours in all. Each teaches one idea with a visual, then gives you one problem built for it. Read the lessons here, then create a free account to practise and keep your progress.
Stage 0Timed set 1
- Joining two islandsFind the island you can already see, then grow outwards from all of it at once until you touch the other.14 min
- Longest mirror subsequenceThe longest palindrome you can make by deleting letters from a word.14 min
- Ladders or bricksWalk along buildings of different heights, climbing each rise with bricks or a ladder, and find the furthest you can get, by giving ladders to the biggest rises.20 min
- Watching every branchPlace the fewest cameras in a tree so that every node is watched, where a camera watches its parent, itself and its children, using three states per node.22 min
- Rain between the wallsWork out how much rain a row of walls can hold, filling layer by layer whenever a taller wall closes a dip.20 min
Stage 1Timed set 2
- A chain reactionBuild a one-way graph from distances, then search from every starting point to find the biggest chain.14 min
- Ring of housesRob houses around a circle with no two neighbours, where the first and last are neighbours too.12 min
- Insert operators to reach a targetPut plus, minus or times between the digits of a string, or nothing at all to join digits, to make an expression equal to a target, tracking the last term so that times is applied correctly.26 min
- The longest climbFind the length of the longest strictly increasing run of values (in order, not necessarily neighbours) by keeping the best tail for each length and searching it.18 min
- Pairs that fill up a kCount pairs whose sum is a multiple of k.12 min
All of Timed practice is free
That’s the whole topic, from the first idea to the mastery stage, with no card needed. Create a free account to practise, keep your progress and carry on to the next topic.
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