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# 0542. 01 Matrix

<https://leetcode.com/problems/01-matrix>

## Description

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:**

![](https://assets.leetcode.com/uploads/2021/04/24/01-1-grid.jpg)

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

**Example 2:**

![](https://assets.leetcode.com/uploads/2021/04/24/01-2-grid.jpg)

```
**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`.

## ac

```java
```