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# 1253. Reconstruct a 2-Row Binary Matrix

<https://leetcode.com/problems/reconstruct-a-2-row-binary-matrix>

## Description

Given the following details of a matrix with `n` columns and `2` rows :

* The matrix is a binary matrix, which means each element in the matrix can be `0` or `1`.
* The sum of elements of the 0-th(upper) row is given as `upper`.
* The sum of elements of the 1-st(lower) row is given as `lower`.
* The sum of elements in the i-th column(0-indexed) is `colsum[i]`, where `colsum` is given as an integer array with length `n`.

Your task is to reconstruct the matrix with `upper`, `lower` and `colsum`.

Return it as a 2-D integer array.

If there are more than one valid solution, any of them will be accepted.

If no valid solution exists, return an empty 2-D array.

**Example 1:**

```
**Input:** upper = 2, lower = 1, colsum = [1,1,1]
**Output:** [[1,1,0],[0,0,1]]
**Explanation:** [[1,0,1],[0,1,0]], and [[0,1,1],[1,0,0]] are also correct answers.
```

**Example 2:**

```
**Input:** upper = 2, lower = 3, colsum = [2,2,1,1]
**Output:** []
```

**Example 3:**

```
**Input:** upper = 5, lower = 5, colsum = [2,1,2,0,1,0,1,2,0,1]
**Output:** [[1,1,1,0,1,0,0,1,0,0],[1,0,1,0,0,0,1,1,0,1]]
```

**Constraints:**

* `1 <= colsum.length <= 10^5`
* `0 <= upper, lower <= colsum.length`
* `0 <= colsum[i] <= 2`

## ac

```java
```