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  1. // HoaiNam
  2. #include <bits/stdc++.h>
  3. #define endl "\n"
  4. #define int long long
  5. #define all(x) x.begin(), x.end()
  6. #define NAME ""
  7. using namespace std;
  8.  
  9. const int N = 1e3 + 1;
  10. const int INF = 1e9;
  11. const int mod = 1e9 + 7;
  12.  
  13. int dx[] = { -1, 0, 1, 0};
  14. int dy[] = {0, 1, 0, -1};
  15.  
  16. int n, m, dist[N][N];
  17. char A[N][N];
  18.  
  19. void bfs() {
  20.     queue<pair<int, int>> q;
  21.     for (int i = 1; i <= n; ++i)
  22.         for (int j = 1; j <= m; ++j) {
  23.             dist[i][j] = INF;
  24.         }
  25.     for (int i = 1; i <= n; ++i)
  26.         for (int j = 1; j <= m; ++j) {
  27.             if (A[i][j] == '1') {
  28.                 q.push({i, j});
  29.                 dist[i][j] = 0;
  30.             }
  31.         }
  32.  
  33.     while (!q.empty()) {
  34.         auto [u, v] = q.front();
  35.         q.pop();
  36.         for (int i = 0; i < 4; ++i) {
  37.             int x = u + dx[i];
  38.             int y = v + dy[i];
  39.             if (x >= 1 && x <= n && y >= 1 && y <= m && dist[x][y] > dist[u][v] + 1) {
  40.                 dist[x][y] = dist[u][v] + 1;
  41.                 q.push({x, y});
  42.             }
  43.         }
  44.     }
  45. }
  46.  
  47. signed main() {
  48.     ios::sync_with_stdio(false);
  49.     cin.tie(nullptr);
  50.  
  51.     if (fopen(NAME".INP", "r")) {
  52.         freopen(NAME".INP", "r", stdin);
  53.         freopen(NAME".OUT", "w", stdout);
  54.     }
  55.  
  56.     cin >> n >> m;
  57.  
  58.     for (int i = 1; i <= n; ++i) {
  59.         for (int j = 1; j <= m; ++j) {
  60.             cin >> A[i][j];
  61.         }
  62.     }
  63.  
  64.     bfs();
  65.  
  66.     int ans = 0;
  67.     for (int i = 1; i <= n; ++i) {
  68.         for (int j = 1; j <= m; ++j) {
  69.             if (dist[i][j] != INF) ans = max(ans, dist[i][j]);
  70.         }
  71.     }
  72.     cout << ans;
  73.  
  74.     // HoaiNam
  75. }
  76.  
Success #stdin #stdout 0.01s 5260KB
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https://ideone.com/EL7R1D
language:
C++14 (gcc 8.3)
created:
2 days ago
visibility:
public

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