Python solution with explanation, easy to understand

  • 0
    class Solution(object):
        def spiralOrder(self, matrix):
            :type matrix: List[List[int]]
            :rtype: List[int]
            if matrix == []:
                return []
            numRows,numCols = len(matrix),len(matrix[0])
            visited = [[False for x in range(numCols)] for y in range(numRows)]
            i,j = 0,0
            res = [matrix[0][0]]
            visited[0][0] = True
            directions = [[0,1],[1,0],[0,-1],[-1,0]] #right,down,left,up
            direct_cnt = 0
            i_pre,j_pre = 0,0
            if numCols == 1:
                direct_cnt += 1
            for x in range(numRows * numCols):
                direction = directions[direct_cnt % 4]
                i,j = i+direction[0],j+direction[1]        
                while i >=0 and i<numRows and j>=0 and j<numCols and visited[i][j] is False:
                    visited[i][j] = True
                    i_pre,j_pre = i,j
                    i,j = i+direction[0],j+direction[1]
                if i <0 or i >= numRows or j < 0 or j > numCols:
                    i,j = i_pre,j_pre
                    direct_cnt += 1
            return res

    Since the directions are always in the order of right,down,left,up, we can use a list to store the directions and use a count to indicate the current direction. if either i or j is out of boundary, that means it's time to change direction. Before next move, i,j should be reset to previous values (Otherwise i or j is out of boundary). Additional visited[][] matrix is used to record if the element has been visited. The total steps should be number of Rows * number of Cols.

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