【leetcode】566. 重塑矩阵（python）

先展成一维数组，再映射成 r 行 c 列 数组

class Solution(object):
    def matrixReshape(self, mat, r, c):
        """
        :type mat: List[List[int]]
        :type r: int
        :type c: int
        :rtype: List[List[int]]
        """
        if not mat:
            return []
        row_mat = len(mat)
        col_mat = len(mat[0])
        res = []
        all_num = []    # note : res = all_num = []  # error !  这样写会占用同一块存储空间
        if row_mat * col_mat == r * c:
            for i in range(row_mat):
                for j in range(col_mat):
                    all_num.append(mat[i][j])   # 展成一维数组，即 flatten操作
            tmp = []
            for k in range(row_mat * col_mat):
                tmp.append(all_num[k])
                if (k + 1) % c == 0:
                    res.append(tmp)
                    tmp = []
        else:
            return mat
        return res

class Solution(object):
    def matrixReshape(self, mat, r, c):
        m, n = len(mat), len(mat[0])
        if m * n != r * c:
            return mat
        ans = [[0] * c for _ in range(r)]
        for x in range(m * n):
            ans[x // c][x % c] = mat[x // n][x % n]
        return ans