# The idea and code example of using the iterator to print the spiral matrix in Python, And the python Matrix

Source: Internet
Author: User

The idea and code example of using the iterator to print the spiral matrix in Python, And the python Matrix

Ideas

A spiral matrix refers to a spiral matrix with numbers increasing from the first line to the right and increasing downward,
To the left, and to the up, so that the cycle.
The spiral matrix is represented by a two-dimensional array. The coordinates (x, y) are (x axis and y axis ).
The clockwise direction of the spiral is-> right, bottom, left, top, which is represented by a numerical value that is x plus 1 lattice (), y plus 1 lattice ), x minus 1 (-1, 0), y minus 1 (0,-1 ).
Coordinates start to walk from (0, 0). When the range is exceeded or the obstacle is encountered, the direction is switched.
To print a spiral matrix, you must first assign values to n * n arrays. According to the rule, each layer is incremented in the order of right-> bottom-> left-> top, therefore, as long as the first number of each layer can be found, the first value is the first number + 4 * n-4 of the previous layer, the cycle of n minus 2 each time.

Code
After the above analysis, the idea is very clear, and the thousand words are not as simple as one code:

`Import itertools def spiral (n, m): _ status = itertools. cycle (['right', 'down', 'left', 'up']) # used for periodic state switching _ movemap = {'right ), 'low': (), 'left' :(-), 'up' :( 0,-1),} pos2no = dict. fromkeys ([(x, y) for x in range (n) for y in range (m)]) _ pos = (0, 0) _ st = next (_ status) for I in range (1, n * m + 1): _ oldpos = _ pos = tuple (map (sum, zip (_ pos, _ movemap [_ st]) # Move if (_ pos not in pos2no) or (pos2no [_ pos]) by status: # Switch direction when the range is exceeded or encounters obstacles _ st = next (_ status) _ pos = tuple (map (sum, zip (_ oldpos, _ movemap [_ st]) pos2no [_ oldpos] = I return pos2no def display_spiral (n, m): pos2no = spiral (n, m) for I in range (m): for j in range (n): print pos2no [(j, I)], '\ t ', print '\ n' print'-'* 30 display_spiral (4, 4) display_spiral (5, 4)`

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