c++ - Rotate NxN Matrix Counter(anti)-Clockwise 90 Degress -


i have 2d matrix m[n][n] need rotate counter-clockwise 90 degrees. have seen many answers clockwise rotation cannot find counter-clockwise. how similar 2 operations?

if reverse order of each individual row , taken rows in opposite order clockwise rotation, count-clockwise rotation.

a b c                  g d               d g                  c f d e f -> clockwise ->  h e b -> reverse -> b e h  -> opposite ->  b e h g h                  f c    rows       c f     ordering     d g  matrix                                                            counter                                                                   clockwise

usually it's easier (and more computationally efficient) clockwise rotation rotation on original matrix in reverse order if have clockwise rotating algorithm available.

1 2 3                9 8 7                 3 6 9 4 5 6 -> reverse  -> 6 5 4 -> clockwise -> 2 5 8 7 8 9    indices     3 2 1                 1 4 7  matrix                                     counter                                            clockwise

you can take 3 clockwise rotations counter clockwise rotation.

though in reality it's easy edit clockwise algorithm purposes directly. i'd use above options if don't care efficiency , don't want work through logic of changing direction of rotation.


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