Given an `m x n` binary matrix `mat`, return the distance of the nearest `0` for each cell.

The distance between two adjacent cells is `1`.

Example 1:

    Input: mat = [[0,0,0],[0,1,0],[0,0,0]]
    Output: [[0,0,0],[0,1,0],[0,0,0]]

Example 2:

    Input: mat = [[0,0,0],[0,1,0],[1,1,1]]
    Output: [[0,0,0],[0,1,0],[1,2,1]]

Constraints:

- `m == mat.length`
- `n == mat[i].length`
- `1 <= m, n <= 104`
- `1 <= m * n <= 104`
- `mat[i][j]` is either `0` or `1`.
- There is at least one `0` in `mat`.