1_A_Gathering_Contestants.cpp

#include <algorithm>
#include <iostream>
#include <cstring>
#include <climits>
#include <cstdio>
#include <cmath>

#include <unordered_map>
#include <vector>
#include <stack>
#include <deque>
#include <queue>
#include <map>
#include <set>
using namespace std;

typedef string str;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> ii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<ll> vll;
typedef map<int, int> mii;
typedef map<ll, ll> mll;
typedef set<int> si;

#define all(x) x.begin(), x.end()
#define sz(x) (int) x.size()
#define fr front()
#define bk back()
#define pb push_back
#define pf push_front
#define ins insert
#define fi first
#define se second

#define FOR(i, a, b, inc) for (int i = a; i < b; i += inc)
#define RFOR(i, a, b, inc) for (int i = b - 1; i >= a; i -= inc)
#define REP(i, a) FOR(i, 0, a, 1)
#define RREP(i, a) RFOR(i, 0, a, 1)
#define each(a, x) for (auto& a: x)

const int INF = 1e9;
const int MOD = 1e9 + 7;

int gcd(int a, int b);
int pow(int a, int b);

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int r, c; cin >> r >> c;
    int prefSum[r + 5][c + 5];
    int grid[r + 5][c + 5];

    memset(prefSum, 0, sizeof(prefSum));
    FOR (i, 1, r + 1, 1) {
        FOR (j, 1, c + 1, 1) {
            char ch; cin >> ch;
            grid[i][j] = ch - '0';
        }
    }

    FOR (i, 1, r + 1, 1) {
        FOR (j, 1, c + 1, 1) {
            prefSum[i][j] = prefSum[i - 1][j] + prefSum[i][j - 1] - prefSum[i - 1][j - 1] + grid[i][j];
        }
    }

    int ans = INT_MAX;
    FOR (k, 1, r + 1, 1) {
        if (prefSum[r][c] % k != 0 || prefSum[r][c] / k > c) continue;
        int leng = prefSum[r][c] / k;

        FOR (i, k, r + 1, 1) {
            FOR (j, leng, c + 1, 1) {
                int cur = prefSum[i][j] - prefSum[i][j - leng] - prefSum[i - k][j] + prefSum[i - k][j - leng];
                ans = min(ans, prefSum[r][c] - cur);
            }
        }
    }

    if (ans == INT_MAX) cout << -1 << '\n';
    else cout << ans << '\n';
}

int gcd(int a, int b) {
    if (b == 0) return a;
    return gcd(b, a%b);
}

int pow(int a, int b) {
    if (b == 0) return 1;
    if (b == 1) return a;
    int x = pow(a, b/2);
    if (b%2 == 0) return x*x;
    return x*x*a;
}