[Daily Leetcode] 566. Reshape the Matrix

Question:

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.

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.

The reshaped matrix need to be filled with all the elements of the original matrix in the same row-traversing order as they were.

If the ‘reshape’ operation with given parameters is possible and legal, output the new reshaped matrix; Otherwise, output the original matrix.

Example 1:

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.

Example 2:

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.

Solution :

class Solution(object):
    def matrixReshape(self, nums, r, c):
        """
        :type nums: List[List[int]]
        :type r: int
        :type c: int
        :rtype: List[List[int]]
        """

        nums1 = []
        nums2 = []
        for i in range(len(nums)):
            nums1 += nums[i]
        if r * c != len(nums1):
            return nums
        else:
            for i in range(r):
                nums2.append(nums1[i*c: i*c + c])
            return nums2

 

Analysis :

The solution showed above is very forthright, but the efficiency, out of my expectation is very high, outnumbering 99.7% solutions submitted.

To judge if the Matrix is reshape-able, this we the first thing we have to do is to judge wether the number of  elements in the matrix equals to r * c, so here we have created a new list which concatenate all the numbers in the Matrix, and then if the result meet the requirement, we’ll come out with some lines aiming at sort the list by number and append it to the new list.

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