P4162 [SCOI2009]最长距离

题目链接：​​传送门​​

从每个点跑spfa
经过障碍距离就加一
看这条路径的长度是不是<=T

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <complex>
#include <algorithm>
#include <climits>
#include <queue>
#include <map>
#include <set>
#include <vector>
#include <iomanip>
#define
#define

using namespace std;
typedef long long ll;
const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
int v[B][B], n, m, t, mp[B][B], dis[B][B];
char opt; double ans;
void wbb(int x, int y) {
  memset(v, 0, sizeof v);
  memset(dis, 0x3f, sizeof dis);
  queue<int> q1, q2; dis[x][y] = mp[x][y];
  q1.push(x); q2.push(y);
  while (!q1.empty()) {
    int xx = q1.front(); q1.pop();
    int yy = q2.front(); q2.pop();
    v[xx][yy] = 0;
    for (int i = 0; i < 4; i++) {
      int fx = xx + dx[i];
      int fy = yy + dy[i];
      if (fx < 1 or fx > n or fy < 1 or fy > m) continue;
      if (dis[fx][fy] > dis[xx][yy] + mp[fx][fy]) {
        dis[fx][fy] = dis[xx][yy] + mp[fx][fy];
        if (!v[fx][fy]) {
          v[fx][fy] = 1;
          q1.push(fx);
          q2.push(fy);
        }
      }
    }
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
      if (dis[i][j] <= t)
        ans = max(ans, sqrt((i - x) * (i - x) + (j - y) * (j - y)));
}

int main(int argc, char const *argv[]) {
  cin >> n >> m >> t;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) {
      cin >> opt;
      if (opt == '0') mp[i][j] = 0;
      else mp[i][j] = 1;
    }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
      wbb(i, j);
  cout << fixed << setprecision(6) << ans << endl;
}