I liked the way Grokking the coding interview organized problems into learnable patterns. However, the course is expensive and the majority of the time the problems are copy-pasted from leetcode. As the explanations on leetcode are usually just as good, the course really boils down to being a glorified curated list of leetcode problems.
So below I made a list of leetcode problems that are as close to grokking problems as possible.
| var groupBy = function(data, key) { // `data` is an array of objects, `key` is the key (or property accessor) to group by | |
| // reduce runs this anonymous function on each element of `data` (the `item` parameter, | |
| // returning the `storage` parameter at the end | |
| return data.reduce(function(storage, item) { | |
| // get the first instance of the key by which we're grouping | |
| var group = item[key]; | |
| // set `storage` for this instance of group to the outer scope (if not empty) or initialize it | |
| storage[group] = storage[group] || []; | |