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# 0750. Number Of Corner Rectangles

<https://leetcode.com/problems/number-of-corner-rectangles>

## Description

Given an `m x n` integer matrix `grid` where each entry is only `0` or `1`, return *the number of **corner rectangles***.

A **corner rectangle** is four distinct `1`'s on the grid that forms an axis-aligned rectangle. Note that only the corners need to have the value `1`. Also, all four `1`'s used must be distinct.

**Example 1:**

![](https://assets.leetcode.com/uploads/2021/06/12/cornerrec1-grid.jpg)

```
**Input:** grid = [[1,0,0,1,0],[0,0,1,0,1],[0,0,0,1,0],[1,0,1,0,1]]
**Output:** 1
**Explanation:** There is only one corner rectangle, with corners grid[1][2], grid[1][4], grid[3][2], grid[3][4].
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2021/06/12/cornerrec2-grid.jpg)

```
**Input:** grid = [[1,1,1],[1,1,1],[1,1,1]]
**Output:** 9
**Explanation:** There are four 2x2 rectangles, four 2x3 and 3x2 rectangles, and one 3x3 rectangle.
```

**Example 3:**

![](https://assets.leetcode.com/uploads/2021/06/12/cornerrec3-grid.jpg)

```
**Input:** grid = [[1,1,1,1]]
**Output:** 0
**Explanation:** Rectangles must have four distinct corners.
```

**Constraints:**

* `m == grid.length`
* `n == grid[i].length`
* `1 <= m, n <= 200`
* `grid[i][j]` is either `0` or `1`.
* The number of `1`'s in the grid is in the range `[1, 6000]`.

## ac

```java
```