0542.cpp

class Solution {
public:
  vector<vector<int>> updateMatrix(vector<vector<int>> &mat) {
    int m = mat.size(), n = mat[0].size();
    vector<vector<int>> dist(m, vector<int>(n, 1e5));

    for (int i = 0; i < m; i++) {
      for (int j = 0; j < n; j++) {
        if (mat[i][j] == 0) {
          dist[i][j] = 0;
        } else {
          if (i > 0)
            dist[i][j] = min(dist[i][j], dist[i - 1][j] + 1);
          if (j > 0)
            dist[i][j] = min(dist[i][j], dist[i][j - 1] + 1);
        }
      }
    }

    for (int i = m - 1; i >= 0; i--) {
      for (int j = n - 1; j >= 0; j--) {
        if (i < m - 1)
          dist[i][j] = min(dist[i][j], dist[i + 1][j] + 1);
        if (j < n - 1)
          dist[i][j] = min(dist[i][j], dist[i][j + 1] + 1);
      }
    }

    return dist;
  }
};