codeforces 679 C

發現其實變量的命名，空格的書寫方式以及花括號的打否非常關鍵，直接影響到心情~

#include <iostream>
#include <fstream>
#include <set>
#include <map>
#include <string>
#include <vector>
#include <bitset>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <cassert>
#include <queue>


typedef long long ll;
typedef long double ld;

using namespace std;
const int MAXN = 510;

int n, k;
int arr[MAXN][MAXN];
int was[MAXN][MAXN];
int cl[MAXN][MAXN];
int nc[MAXN * MAXN];
int lst[MAXN * MAXN];
int tm;
int cc;
int cnt[MAXN * MAXN];
int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};

void dfs(int x, int y, int c) {
    was[x][y] = 1;
    cl[x][y] = c;
    ++cnt[c];
    for (int i = 0; i < 4; ++i) {
        int nx = x + dx[i];
        int ny = y + dy[i];
        if (!arr[nx][ny] && !was[nx][ny])
            dfs(nx, ny, c);
    }
}

int add(int x, int y) {
    if (arr[x][y])
        return 0;
    if (lst[cl[x][y]] == tm)
        return 0;
    lst[cl[x][y]] = tm;
    return cnt[cl[x][y]] - nc[cl[x][y]];
}


int main() {
    scanf("%d%d", &n, &k);
    for (int i = 0; i <= n + 1; ++i)
        for (int j = 0; j <= n + 1; ++j)
            arr[i][j] = 1;
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= n; ++j) {
            char c;
            scanf(" %c", &c);
            if (c == '.')
                arr[i][j] = 0;
            else
                arr[i][j] = 1;
        }
    cc = 0;
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= n; ++j) {
            if (!arr[i][j] && !was[i][j]) {
                dfs(i, j, cc++);
            }
        }
    int ans = 0;
    for (int i = 0; i < cc; ++i)
        ans = max(ans, cnt[i]);
    for (int i = 1; i <= n - k + 1; ++i) {
        memset(nc, 0, sizeof(nc[0]) * cc);
        for (int j = i; j < i + k; ++j)
            for (int j1 = 1; j1 <= k; ++j1)
                if (!arr[j][j1])
                    ++nc[cl[j][j1]];
        for (int j = 1; j <= n - k + 1; ++j) {
            ++tm;
            int now = k * k;
            for (int i1 = i; i1 < i + k; ++i1)
                now += add(i1, j - 1), now += add(i1, j + k);
            for (int j1 = j; j1 < j + k; ++j1)
                now += add(i - 1, j1), now += add(i + k, j1);
            ans = max(ans, now);
            for (int i1 = i; i1 < i + k; ++i1)
                if (!arr[i1][j])
                    --nc[cl[i1][j]];
            for (int i1 = i; i1 < i + k; ++i1)
                if (!arr[i1][j + k])
                    ++nc[cl[i1][j + k]];
        }
    }
    cout << ans << "\n";
    return 0;
}