1351. Count Negative Numbers in a Sorted Matrix

Problem

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?

Solution (Java)

class Solution {
    public int countNegatives(int[][] grid) {
        int count = 0;
        for (int[] row : grid) {
            for (int v : row) {
                if (v < 0) {
                    count++;
                }
            }
        }
        return count;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).