bitset

#include<cstdio>
#include<algorithm>
#include<bitset>
#include<iostream>
using std::cin;
using std::cout;
using std::endl;
using std::bitset; 
const int maxn = 1e6;
bitset<100000> bt[2]; 
int a[maxn];
int n;
int main(){
    cin >> n;
    int m = 0;
    for(int i = 1 ; i <= n ; i ++) {
        cin >> a[i];
        m += a[i];
    }
    for(int i = 1 ; i <= n ; i ++) {
        bt[0] = bt[1] | (bt[1] << a[i]);
        bt[1] = bt[0];
        bt[1][a[i]] = 1;
    }
    for(int i = 1 ; i <= m ; i ++) {
        if(bt[1][i]) cout<<"exist : "<<i<<endl;
    }
    return 0;
}

子矩阵值最大

枚举竖行上下界，横行记录最大值和次大值

二分答案：枚举值，大于的为一，小于为0

                 找全是1的矩阵O(n^3)->bitset：数1的个数

logn*(n^2+(n^3)/32)