1351\. Count Negative Numbers in a Sorted Matrix

Easy

Given a `m x n` matrix `grid` which is sorted in non-increasing order both row-wise and column-wise, return _the number of **negative** numbers in_ `grid`.

**Example 1:**

**Input:** grid = [[4,3,2,-1],[3,2,1,-1],[1,1,-1,-2],[-1,-1,-2,-3]]

**Output:** 8

**Explanation:** There are 8 negatives number in the matrix.

**Example 2:**

**Input:** grid = [[3,2],[1,0]]

**Output:** 0

**Constraints:**

*   `m == grid.length`
*   `n == grid[i].length`
*   `1 <= m, n <= 100`
*   `-100 <= grid[i][j] <= 100`

**Follow up:** Could you find an `O(n + m)` solution?