Solve InterviewCake's "find rotation point" problem
Write a function that accepts a rotated cycle of alphabetically sorted strings and returns the index what should be the first element if the elements were not rotated.
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								scratch/deepmind/part_two/find-rotation-point.ts
									
										
									
									
									
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								scratch/deepmind/part_two/find-rotation-point.ts
									
										
									
									
									
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							|  | @ -0,0 +1,68 @@ | ||||||
|  | function findRotationPoint(xs: Array<string>): number { | ||||||
|  |   // Find the rotation point in the vector.
 | ||||||
|  |   let beg = 0; | ||||||
|  |   let end = xs.length - 1; | ||||||
|  | 
 | ||||||
|  |   while (beg != end) { | ||||||
|  |     let mid = beg + Math.floor((end - beg) / 2); | ||||||
|  | 
 | ||||||
|  |     if (beg === mid) { | ||||||
|  |       return xs[beg] < xs[end] ? beg : end; | ||||||
|  |     } | ||||||
|  | 
 | ||||||
|  |     if (xs[end] <= xs[mid]) { | ||||||
|  |       beg = mid; | ||||||
|  |       end = end; | ||||||
|  |     } else { | ||||||
|  |       beg = beg; | ||||||
|  |       end = mid; | ||||||
|  |     } | ||||||
|  |   } | ||||||
|  | 
 | ||||||
|  |   return beg; | ||||||
|  | } | ||||||
|  | 
 | ||||||
|  | // Tests
 | ||||||
|  | let desc; | ||||||
|  | let actual; | ||||||
|  | let expected; | ||||||
|  | 
 | ||||||
|  | desc = "small array one"; | ||||||
|  | actual = findRotationPoint(["cape", "cake"]); | ||||||
|  | expected = 1; | ||||||
|  | assertEquals(actual, expected, desc); | ||||||
|  | 
 | ||||||
|  | desc = "small array two"; | ||||||
|  | actual = findRotationPoint(["cake", "cape"]); | ||||||
|  | expected = 0; | ||||||
|  | assertEquals(actual, expected, desc); | ||||||
|  | 
 | ||||||
|  | desc = "medium array"; | ||||||
|  | actual = findRotationPoint(["grape", "orange", "plum", "radish", "apple"]); | ||||||
|  | expected = 4; | ||||||
|  | assertEquals(actual, expected, desc); | ||||||
|  | 
 | ||||||
|  | desc = "large array"; | ||||||
|  | actual = findRotationPoint([ | ||||||
|  |   "ptolemaic", | ||||||
|  |   "retrograde", | ||||||
|  |   "supplant", | ||||||
|  |   "undulate", | ||||||
|  |   "xenoepist", | ||||||
|  |   "asymptote", | ||||||
|  |   "babka", | ||||||
|  |   "banoffee", | ||||||
|  |   "engender", | ||||||
|  |   "karpatka", | ||||||
|  |   "othellolagkage" | ||||||
|  | ]); | ||||||
|  | expected = 5; | ||||||
|  | assertEquals(actual, expected, desc); | ||||||
|  | 
 | ||||||
|  | function assertEquals(a, b, desc) { | ||||||
|  |   if (a === b) { | ||||||
|  |     console.log(`${desc} ... PASS`); | ||||||
|  |   } else { | ||||||
|  |     console.log(`${desc} ... FAIL: ${a} != ${b}`); | ||||||
|  |   } | ||||||
|  | } | ||||||
|  | @ -16,7 +16,7 @@ | ||||||
| ** DONE Cafe Order Checker | ** DONE Cafe Order Checker | ||||||
| ** DONE In-Place Shuffle | ** DONE In-Place Shuffle | ||||||
| * Sorting, searching, and logarithms | * Sorting, searching, and logarithms | ||||||
| ** TODO Find Rotation Point | ** DONE Find Rotation Point | ||||||
| ** TODO Find Repeat, Space Edition | ** TODO Find Repeat, Space Edition | ||||||
| ** TODO Top Scores | ** TODO Top Scores | ||||||
| ** TODO Merging Meeting Times | ** TODO Merging Meeting Times | ||||||
|  |  | ||||||
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