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BP934 |
| If "distance" is taken to be the sum of horizontal and vertical distances between points, the 3 points are equidistant from each other vs. not so. |
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COMMENTS
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In other words, we take the distance between points (a,b) and (c,d) to be equal to |c-a| + |d-b|, or, in other words, the distance of the shortest path between points that travels along grid lines. In mathematics, this way of measuring distance is called the 'taxicab' or 'Manhattan' metric. The points on the left hand side form equilateral triangles in this metric.
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An alternate (albeit more convoluted) solution that someone may arrive at for this Problem is as follows: The triangles formed by the points on the left have some two points diagonal to each other (in the sense of bishops in chess), and considering the corresponding edge as their base, they also have an equal height. However, this was proven to be equivalent to the Manhattan distance answer by Sridhar Ramesh. Here is the proof:
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An equilateral triangle amounts to points A, B, and C such that B and C lie on a circle of some radius centered at A, and the chord from B to C is as long as this radius.
A Manhattan circle of radius R is a turned square, ♢, where the Manhattan distance between any two points on opposite sides is 2R, and the Manhattan distance between any two points on adjacent sides is the larger distance from one of those points to the corner connecting those sides. Thus, to get two of these points to have Manhattan distance R, one of them must be a midpoint of one side of the ♢ (thus, bishop-diagonal from its center) and the other can then be any point on an adjacent side of the ♢ making an acute triangle with the aforementioned midpoint and center. |
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CROSSREFS
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Adjacent-numbered pages:
BP929 BP930 BP931 BP932 BP933  *  BP935 BP936 BP937 BP938 BP939
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KEYWORD
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hard, allsorted, solved, left-finite, right-finite, perfect, pixelperfect, unorderedtriplet, finishedexamples
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CONCEPT
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triangle (info | search)
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WORLD
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3_dots_on_square_grid [smaller | same | bigger]
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AUTHOR
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Leo Crabbe
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BP935 |
| Shapes have equal area vs. not so. |
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BP937 |
| Shapes have equal perimeter vs. not so. |
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BP945 |
| Cube number of dots vs. non-cube number of dots. |
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BP949 |
| Two unique distances between points vs. three unique distances between points. |
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BP956 |
| Nested pairs of brackets vs. other arrangement of brackets (some open brackets are not closed or there are extra closing brackets). |
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COMMENTS
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Examples on the left are also known as "Dyck words". |
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REFERENCE
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https://en.wikipedia.org/wiki/Dyck_language |
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CROSSREFS
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Adjacent-numbered pages:
BP951 BP952 BP953 BP954 BP955  *  BP957 BP958 BP959 BP960 BP961
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KEYWORD
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easy, nice, precise, allsorted, unwordable, notso, sequence, traditional, inductivedefinition, preciseworld, left-listable, right-listable
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CONCEPT
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recursion (info | search)
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AUTHOR
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Aaron David Fairbanks
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CROSSREFS
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Adjacent-numbered pages:
BP957 BP958 BP959 BP960 BP961  *  BP963 BP964 BP965 BP966 BP967
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KEYWORD
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precise, allsorted, minimal, dual, blackwhite, gap, left-finite, right-finite, left-full, right-full, left-null, finished, preciseworld, unstableworld
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WORLD
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[smaller | same | bigger] zoom in left (blank_image) | zoom in right (black_image)
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AUTHOR
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Leo Crabbe
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BP977 |
| Two of the same object are enclosed in the same space (there is a path between them) vs. not so. |
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BP986 |
| Palindromes vs. not palindromes. |
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COMMENTS
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All examples in this Problem are sequences of graphic symbols. In this Problem, a "palindrome" is taken to be an ordered sequence which is the same read left-to-right as it is read right-to-left. A more formal solution to this Problem could be: "Sequences which are invariant under a permutation which swaps first and last entries, second and second last entries, third and third last entries, ... and so on vs. sequences which are not invariant under the aforementioned permutamation." |
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CROSSREFS
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Adjacent-numbered pages:
BP981 BP982 BP983 BP984 BP985  *  BP987 BP988 BP989 BP990 BP991
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KEYWORD
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nice, precise, allsorted, notso, sequence, traditional
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CONCEPT
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element_wise_symmetry (info | search), identical (info | search), sequence (info | search), same_shape (info | search), same (info | search), symmetry (info | search)
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WORLD
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zoom in left | zoom in right
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AUTHOR
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Jago Collins
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BP988 |
| Number of dots is a power of 2 vs. not so. |
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