Short Problem Definition:
You are given a 2D matrix, a, of dimension MxN and a positive integer R. You have to rotate the matrix R times and print the resultant matrix. Rotation should be in anti-clockwise direction.
Link
Complexity:
time complexity is O(N×M)
space complexity is O(NxM)
Execution:
There is just lots of code, but the actual solution is pretty simple. I first extract layers, to simplify the logic. Then, I rotate the layers similarly to the Codility Rotation challenge.
Solution:
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def reverse(arr, i, j): for idx in xrange((j - i + 1) / 2): arr[i + idx], arr[j - idx] = arr[j - idx], arr[i + idx]def rotateList(A, K): # performs a right rotation # K needs to be adjusted to len(A) - K for left rotation l = len(A) K %= len(A) reverse(A, l - K, l - 1) reverse(A, 0, l - K - 1) reverse(A, 0, l - 1) return Adef rotateLayers(N, M, R, layers): for layer in layers: rotateList(layer, len(layer) - R)def rotateMatrix(M, N, R, mat): # generate a list of layers l = int(min(N, M) // 2) layers = [[] for _ in range(l)] for level in xrange(l): top = (N - 1) - 2 * level side = (M - 1) - 2 * level for i in range(top): # right layers[level].append(mat[level][level + i]) for j in range(side): # down layers[level].append(mat[level + j][level + top]) for i in range(top): # left layers[level].append(mat[level + side][level + top - i]) for j in range(side): # up layers[level].append(mat[level + side - j][level]) # rotate each layer rotateLayers(N, M, R, layers) # fill the layers back in for level in range(l): top = (N - 1) - 2 * level side = (M - 1) - 2 * level for i in xrange(top): mat[level][level + i] = layers[level].pop(0) # right for j in range(side): mat[level + j][level + top] = layers[level].pop(0) # down for i in range(top): mat[level + side][level + top - i] = layers[level].pop(0) # left for j in range(side): mat[level + side - j][level] = layers[level].pop(0) # updef main(): M, N, R = map(int, raw_input().split()) mat = [] for i in range(M): mat.append(list(map(int, raw_input().split()))) rotateMatrix(M, N, R, mat) # print the rotated matrix for row in range(M): for col in range(N): print mat[row][col], printif __name__ == '__main__': main() |
