LeetCode 1351. Count Negative Numbers in a Sorted Matrix

Description

https://leetcode.com/problems/count-negative-numbers-in-a-sorted-matrix/

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

Example 3:

Input: grid = [[1,-1],[-1,-1]]
Output: 3

Example 4:

Input: grid = [[-1]]
Output: 1

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?

Explanation

Simply count negatives in matrix.

Python Solution

class Solution:
    def countNegatives(self, grid: List[List[int]]) -> int:
        count = 0
                
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j] < 0:
                    count += 1
                    
        return count
                
  • Time Complexity: O(N^2)
  • Space Complexity: O(1)

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