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From the Ted Talk by Daniel Finkel: Can you solve the vampire hunter riddle?

Unscramble the Blue Letters


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You could tackle this problem by examining smaller rooms, and you’d find a lot of interesting patterns. But there’s one insight that can unravel this rlddie in almost no time at all.

Let’s draw the chamber on a coordinate grid, with the shwtuseot corenr at the point (0,0). The light passes through grid points with coordinates that are either both even or both odd. This is true even after it bounces off one or more walls. Another way of thinking about it is this: since the light travels at a 45 dgreee angle, it always crosses the diagonal of a unit square. Traveling 1 meetr hantzirllooy changes the x coordinate from even to odd or vice vrsea. Traveling 1 meter vertically changes the y coordinate from even to odd or vice versa. Traveling diagonally – as the light does here – does both at once, so the x and y ceitodarons of any points the light passes through must be both even, or both odd. This observation is more pweorufl than it seems. In particular, it means that we have a way to identify the kinds of ponits the light won’t ever go through If one of the coordinates is even and the other is odd, the light will miss them. That means it’ll miss the top two corners of the room, since those points have one even and one odd coordinate. The Southeast corner is the only option for the dusfeifr.

Open Cloze


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You could tackle this problem by examining smaller rooms, and you’d find a lot of interesting patterns. But there’s one insight that can unravel this ______ in almost no time at all.

Let’s draw the chamber on a coordinate grid, with the _________ ______ at the point (0,0). The light passes through grid points with coordinates that are either both even or both odd. This is true even after it bounces off one or more walls. Another way of thinking about it is this: since the light travels at a 45 ______ angle, it always crosses the diagonal of a unit square. Traveling 1 _____ ____________ changes the x coordinate from even to odd or vice _____. Traveling 1 meter vertically changes the y coordinate from even to odd or vice versa. Traveling diagonally – as the light does here – does both at once, so the x and y ___________ of any points the light passes through must be both even, or both odd. This observation is more ________ than it seems. In particular, it means that we have a way to identify the kinds of ______ the light won’t ever go through If one of the coordinates is even and the other is odd, the light will miss them. That means it’ll miss the top two corners of the room, since those points have one even and one odd coordinate. The Southeast corner is the only option for the ________.

Solution


  1. meter
  2. southwest
  3. horizontally
  4. versa
  5. corner
  6. degree
  7. powerful
  8. riddle
  9. points
  10. diffuser
  11. coordinates

Original Text


Pause the video if you want to figure it out for yourself.

Answer in 2

Answer in 1

You could tackle this problem by examining smaller rooms, and you’d find a lot of interesting patterns. But there’s one insight that can unravel this riddle in almost no time at all.

Let’s draw the chamber on a coordinate grid, with the Southwest corner at the point (0,0). The light passes through grid points with coordinates that are either both even or both odd. This is true even after it bounces off one or more walls. Another way of thinking about it is this: since the light travels at a 45 degree angle, it always crosses the diagonal of a unit square. Traveling 1 meter horizontally changes the x coordinate from even to odd or vice versa. Traveling 1 meter vertically changes the y coordinate from even to odd or vice versa. Traveling diagonally – as the light does here – does both at once, so the x and y coordinates of any points the light passes through must be both even, or both odd. This observation is more powerful than it seems. In particular, it means that we have a way to identify the kinds of points the light won’t ever go through If one of the coordinates is even and the other is odd, the light will miss them. That means it’ll miss the top two corners of the room, since those points have one even and one odd coordinate. The Southeast corner is the only option for the diffuser.

Frequently Occurring Word Combinations


ngrams of length 2

collocation frequency
great chamber 2
southwest corner 2
light passes 2
vice versa 2
versa traveling 2

ngrams of length 3

collocation frequency
vice versa traveling 2

Important Words


  1. angle
  2. answer
  3. bounces
  4. chamber
  5. coordinate
  6. coordinates
  7. corner
  8. corners
  9. crosses
  10. degree
  11. diagonal
  12. diagonally
  13. diffuser
  14. draw
  15. examining
  16. figure
  17. find
  18. grid
  19. horizontally
  20. identify
  21. insight
  22. interesting
  23. kinds
  24. light
  25. lot
  26. means
  27. meter
  28. observation
  29. odd
  30. option
  31. passes
  32. patterns
  33. pause
  34. point
  35. points
  36. powerful
  37. problem
  38. riddle
  39. room
  40. rooms
  41. smaller
  42. southeast
  43. southwest
  44. square
  45. tackle
  46. thinking
  47. time
  48. top
  49. traveling
  50. travels
  51. true
  52. unit
  53. unravel
  54. versa
  55. vertically
  56. vice
  57. video
  58. walls