13.7 同時發生：讀舊表、寫新表

#include <bits/stdc++.h>
using namespace std;

// 四鄰格的方向表：上、下、左、右
const int dr[4] = {-1, 1, 0, 0};
const int dc[4] = {0, 0, -1, 1};

int main() {
    int R, C, k, m;
    cin >> R >> C >> k >> m;
    vector<vector<int>> population(R, vector<int>(C));
    for (int r = 0; r < R; r++)
        for (int c = 0; c < C; c++) cin >> population[r][c];

    for (int day = 0; day < m; day++) {
        vector<vector<int>> outgoing(R, vector<int>(C));   // 每座城市今天向每個鄰居遷出多少人
        vector<vector<int>> next = population;             // 新的一張表，從舊表複製開始
        for (int r = 0; r < R; r++)
            for (int c = 0; c < C; c++)
                if (population[r][c] != -1)
                    outgoing[r][c] = population[r][c] / k;

        for (int r = 0; r < R; r++) {
            for (int c = 0; c < C; c++) {
                if (population[r][c] == -1) continue;      // 不是城市
                for (int d = 0; d < 4; d++) {
                    const int nr = r + dr[d];
                    const int nc = c + dc[d];
                    if (nr < 0 || nr >= R || nc < 0 || nc >= C) continue;   // 出界不遷
                    if (population[nr][nc] == -1) continue;                 // 鄰格不是城市不遷
                    next[r][c] -= outgoing[r][c];          // 讀舊表 population、寫新表 next
                    next[nr][nc] += outgoing[r][c];
                }
            }
        }
        population.swap(next);                             // 一天結束：新表變成舊表
    }

    int minimum = INT_MAX;
    int maximum = -1;
    for (int r = 0; r < R; r++) {
        for (int c = 0; c < C; c++) {
            if (population[r][c] == -1) continue;
            minimum = min(minimum, population[r][c]);
            maximum = max(maximum, population[r][c]);
        }
    }
    cout << minimum << '\n' << maximum << '\n';
    return 0;
}