Description
有一个N*M的01矩阵，现在你可以的任意交换其中的列，要求找一个最大的仅由1组成的矩阵。 N<=15000,M<=1500 1 ≤ N ≤ 15000 1 ≤ M ≤ 1500 30% of the test cases will have N,M ≤ 1024Input
N,M 以下N行每行M个字符。Output
Sample Input
10 6001010
111110
011110
111110
011110
111111
110111
110111
000101
010101
Sample Output
21Hint
By permuting the columns such that columns 2,4 and 5 are adjacent you have a rectangle of area
21 (rows 2-8 and columns 2, 4, 5).
