// free lessons
learn the patterns interviews actually test.
Every lesson is one small skill with worked examples, the common trap, and a drill. Read them free; practise them with Awel when you want feedback.
hash maps
key-value, lookup, insert, update
70 lessonstwo pointers
pairs, partitions, opposite or same direction
70 lessonssliding window
contiguous ranges, expand, shrink
65 lessonsstacks
LIFO, push, pop, representation
114 lessons