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flatten an array
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| # Let's set up a quick and dirty test framework | |
| # a helper to define the tests | |
| expect = (expected, input) -> | |
| [expected, input] | |
| # an array equivalence test | |
| areSameArrays = (left, right) -> | |
| return no unless left.length is right.length | |
| for i of left | |
| return no unless left[i] is right[i] | |
| yes | |
| # run a single test | |
| runTest = (test, fn) -> | |
| result = fn test[1] | |
| if areSameArrays test[0], result | |
| yes | |
| else | |
| console.log "Expected:", test[0], "saw", result, "on input", test[1] | |
| no | |
| # run the suite of tests | |
| runTests = (tests, fn) -> | |
| pass = 0 | |
| fail = 0 | |
| for test in tests | |
| if runTest test, fn | |
| pass += 1 | |
| else | |
| fail += 1 | |
| console.log "#{tests.length} tests run, #{pass} passed, #{fail} failed" | |
| # the various tests to run | |
| tests = [ | |
| # trivial cases | |
| expect [], [] | |
| expect [1], [1] | |
| expect [1], [[[[1]]]] | |
| expect [1, 2], [1, 2] | |
| # starting to get interesting | |
| expect [1, 2, 3], [1, [2, [3]]] | |
| expect [1, 2, 3, 4], [[1, []], [2], [[], [3, [4]]]] | |
| expect [1, 2, 3], [[[1], 2], 3] | |
| # the given examples | |
| expect [1, 2, 3, 4], [[1,2,[3]],4] | |
| ] | |
| # the implementation | |
| # we'll use a husk-and-kernel method to force tail recursion | |
| flattenKernel = (previous, remaining) -> | |
| return previous if remaining.length is 0 | |
| here = if Array.isArray remaining[0] | |
| # depth-first recursive call | |
| flattenKernel previous, remaining[0] | |
| else | |
| previous.concat remaining[0] | |
| flattenKernel here, remaining[1..] | |
| flatten = (array) -> | |
| flattenKernel [], array | |
| runTests tests, flatten |
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