BFS进阶刷题

P2658 汽车拉力比赛

#include <iostream>
#include <queue>
#include <climits>
#include <cstring>
using namespace std;
#define int long long
int n, m;
int high[505][505];
int flag[505][505];
int dx[] = {1, 0, -1, 0};
int dy[] = {0, -1, 0, 1};
int count;
int dis[505][505];
int startx, starty;
bool bfs(int mid)
{
    int sum = 1;
    memset(dis, -1, sizeof dis);
    queue<pair<int, int>> q;
    q.push({startx, starty});
    dis[startx][starty] = 0;
    if (sum == count)
    {
        return true;
    }
    while (!q.empty())
    {
        auto t = q.front();
        q.pop();
        for (int i = 0; i < 4; i++)
        {
            int nx = t.first + dx[i];
            int ny = t.second + dy[i];
            if (nx < 1 || ny < 1 || nx > n || ny > m)
            {
                continue;
            }
            if (dis[nx][ny] != -1)
            {
                continue;
            }
            int nd = abs(high[nx][ny] - high[t.first][t.second]);
            if (nd <= mid)
            {

                dis[nx][ny] = dis[t.first][t.second] + 1;
                q.push({nx, ny});
                if (flag[nx][ny] == 1)
                {
                    sum++;
                    if (sum == count)
                    {
                        return true;
                    }
                }
            }
        }
    }
    return false;
}
signed main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
        {
            cin >> high[i][j];
        }
    }
    count = 0;
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
        {
            cin >> flag[i][j];
            if (flag[i][j] == 1)
            {
                count++;
                if (startx == 0)
                {
                    startx = i;
                    starty = j;
                }
            }
        }
    }
    int left = -1;
    int right = INT_MAX;
    while (left + 1 < right)
    {
        int mid = (left + right) / 2;
        if (bfs(mid))
        {
            right = mid;
        }
        else
        {
            left = mid;
        }
    }
    cout << right;
    return 0;
}