题意：M x N 的01矩阵(1 ≤ N,M ≤ 1000)，任意两列可以交换，求由1组成的最大子矩阵的面积。
题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2830
——>>枚举每行作为子矩阵的底，用个缓存数组拿下1的高度，排序。。
时间复杂度：O(N * M * log(M))
#include <cstdio>
#include <cstring>
#include <algorithm>using std::sort;
using std::max;const int MAXN = 1000 + 10;int N, M;
int h[MAXN], buf[MAXN];
int ret;int main()
{char ch;while (scanf("%d%d", &N, &M) == 2){ret = 0;memset(h, 0, sizeof(h));for (int i = 1; i <= N; ++i){getchar();for (int j = 1; j <= M; ++j){ch = getchar();if (ch == '1'){++h[j];}else{h[j] = 0;}}memcpy(buf, h, sizeof(h));sort(buf + 1, buf + 1 + M);for (int j = 1; j <= M; ++j){ret = max(ret, (M - j + 1) * buf[j]);}}printf("%d\n", ret);}return 0;
}