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:

**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:

**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:

**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 either0
or1
.The number of
1
's in the grid is in the range[1, 6000]
.
ac
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