diff --git a/scratch/deepmind/part_two/recursive-string-permutations.ts b/scratch/deepmind/part_two/recursive-string-permutations.ts new file mode 100644 index 000000000..cb930d9ad --- /dev/null +++ b/scratch/deepmind/part_two/recursive-string-permutations.ts @@ -0,0 +1,85 @@ +// Returns a new string comprised of every characters in `xs` except for the +// character at `i`. +function everyOtherChar(xs: string, i: number): string[] { + const result = []; + + for (let j = 0; j < xs.length; j += 1) { + if (i !== j) { + result.push(xs[j]); + } + } + + return [xs[i], result.join('')]; +} + +function getPermutations(xs: string): Set { + if (xs === '') { + return new Set(['']); + } + + const result: Set = new Set; + + for (let i = 0; i < xs.length; i += 1) { + const [char, rest] = everyOtherChar(xs, i); + const perms = getPermutations(rest); + + for (const perm of perms) { + result.add(char + perm); + } + } + + return result; +} + +// Tests +let desc = 'empty string'; +let input = ''; +let actual = getPermutations(input); +let expected = new Set(['']); +assert(isSetsEqual(actual, expected), desc); + +desc = 'one character string'; +input = 'a'; +actual = getPermutations(input); +expected = new Set(['a']); +assert(isSetsEqual(actual, expected), desc); + +desc = 'two character string'; +input = 'ab'; +actual = getPermutations(input); +expected = new Set(['ab', 'ba']); +assert(isSetsEqual(actual, expected), desc); + +desc = 'three character string'; +input = 'abc'; +actual = getPermutations(input); +expected = new Set(['abc', 'acb', 'bac', 'bca', 'cab', 'cba']); +assert(isSetsEqual(actual, expected), desc); + +desc = 'four character string'; +input = 'abca'; +actual = getPermutations(input); +expected = new Set([ + 'abca', 'abac', 'acba', 'acab', 'aabc', 'aacb', 'baca', 'baac', 'bcaa', + 'bcaa', 'baac', 'baca', 'caba', 'caab', 'cbaa', 'cbaa', 'caab', 'caba', + 'aabc', 'aacb', 'abac', 'abca', 'acab', 'acba' +]); +assert(isSetsEqual(actual, expected), desc); + +function isSetsEqual(as, bs) { + if (as.size !== bs.size) { + return false; + } + for (let a of as) { + if (!bs.has(a)) return false; + } + return true; +} + +function assert(condition, desc) { + if (condition) { + console.log(`${desc} ... PASS`); + } else { + console.log(`${desc} ... FAIL`); + } +} diff --git a/scratch/deepmind/part_two/todo.org b/scratch/deepmind/part_two/todo.org index ee91e4755..ba128bb82 100644 --- a/scratch/deepmind/part_two/todo.org +++ b/scratch/deepmind/part_two/todo.org @@ -28,7 +28,7 @@ ** DONE MeshMessage ** DONE Find Repeat, Space Edition BEAST MODE * Dynamic programming and recursion -** TODO Recursive String Permutations +** DONE Recursive String Permutations ** TODO Compute nth Fibonacci Number ** TODO Making Change ** TODO The Cake Thief