leetcode542 01 Matrix

思路：

多个起点的bfs。

实现：

 class Solution
 {
 public:
     vector<vector<int>> updateMatrix(vector<vector<int>>& matrix)
     {
         int n = matrix.size(), m = matrix[].size();
         vector<vector<int>> vis(n, vector<int>(m, ));
         vector<vector<int>> d(n, vector<int>(m, 0x3f3f3f3f));
         queue<pair<int, int>> q;
         int dx[] = {, , -, }, dy[] = {, , , -};
         for (int i = ; i < n; i++)
         {
             for (int j = ; j < m; j++)
             {
                 if (matrix[i][j] == )
                 {
                     q.push(pair<int, int>(i, j));
                     vis[i][j] = ;
                     d[i][j] = ;
                 }
             }
         }
         while (!q.empty())
         {
             pair<int, int> tmp = q.front();
             q.pop();
             int x = tmp.first, y = tmp.second;
             for (int i = ; i < ; i++)
             {
                 int nx = x + dx[i], ny = y + dy[i];
                 if (nx >=  && nx < n && ny >=  && ny < m && !vis[nx][ny])
                 {
                     vis[nx][ny] = ;
                     d[nx][ny] = d[x][y] + ;
                     q.push(pair<int, int>(nx, ny));
                 }
             }
         }
         return d;
     }
 };