updateMatrix.cpp

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

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

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