reshape-the-matrix.py

# -*- coding:utf-8 -*-


# In MATLAB, there is a very useful function called 'reshape', which can reshape a matrix into a new one with different size but keep its original data.
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#
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# You're given a matrix represented by a two-dimensional array, and two positive integers r and c representing the row number and column number of the wanted reshaped matrix, respectively.
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#  The reshaped matrix need to be filled with all the elements of the original matrix in the same row-traversing order as they were.
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# If the 'reshape' operation with given parameters is possible and legal, output the new reshaped matrix; Otherwise, output the original matrix.
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# Example 1:
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# Input: 
# nums = 
# [[1,2],
#  [3,4]]
# r = 1, c = 4
# Output: 
# [[1,2,3,4]]
# Explanation:The row-traversing of nums is [1,2,3,4]. The new reshaped matrix is a 1 * 4 matrix, fill it row by row by using the previous list.
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# Example 2:
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# Input: 
# nums = 
# [[1,2],
#  [3,4]]
# r = 2, c = 4
# Output: 
# [[1,2],
#  [3,4]]
# Explanation:There is no way to reshape a 2 * 2 matrix to a 2 * 4 matrix. So output the original matrix.
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# Note:
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# The height and width of the given matrix is in range [1, 100].
# The given r and c are all positive.
#


class Solution(object):
    def matrixReshape(self, nums, r, c):
        """
        :type nums: List[List[int]]
        :type r: int
        :type c: int
        :rtype: List[List[int]]
        """
        length = 0
        res = []
        
        # flatten the original matrix
        flattend_nums = [num for row in nums for num in row]
        
        if r * c != len(flattend_nums):
            return nums # cannot reshape
        
        start = 0
        while start <= len(flattend_nums) - c:
            res.append(flattend_nums[start : start + c])
            start += c
            
        return res