Reshape the Matrix

可以用额外空间，这样逻辑的思考没有那么复杂了，当然不用额外空间也可以做

class Solution(object):
    def matrixReshape(self, nums, r, c):
        """
        :type nums: List[List[int]]
        :type r: int
        :type c: int
        :rtype: List[List[int]]
        """
        n = len(nums)
        if not n:
            return []
        m = len(nums[0])
        if not m:
            return []

        if n * m != r * c:
            return nums

        nums = reduce(operator.add, nums)
        result = []
        cur = 0
        for i in xrange(r):
            result.append(nums[cur : cur + c])
            cur += c
        return result

理论上没有额外空间的算法

class Solution(object):
    def matrixReshape(self, nums, r, c):
        """
        :type nums: List[List[int]]
        :type r: int
        :type c: int
        :rtype: List[List[int]]
        """
        n = len(nums)
        if not n:
            return []
        m = len(nums[0])
        if not m:
            return []

        if n * m != r * c:
            return nums

        count = 0
        result = [[0] * c for _ in xrange(r)]
        for i in xrange(n):
            for j in xrange(m):
                result[count / c][count % c] = nums[i][j]
                count += 1

        return result