[Solved] 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.

Question

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?

Python Solution

class Solution:
    def countNegatives(self, grid: List[List[int]]) -> int:
        m=len(grid)
        n=len(grid[0])

        r,c,neg_count = 0,n-1,0

        while r<m and c>=0:
            if grid [r][c]<0:
                neg_count = neg_count + m-r
                c-=1
            else:
                r+=1
        return (neg_count)