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1476. Count Negative Numbers In A Sorted Matrix

Array Binary Search Matrix

Problem - 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?

Solutions

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class Solution:
    def countNegatives(self, grid: List[List[int]]) -> int:
        m, n = len(grid), len(grid[0])
        i, j = m - 1, 0
        result = 0

        while i >= 0 and j < n:
            if grid[i][j] >= 0:
                j += 1
            else:
                result += n - j
                i -= 1

        return result

Submission Stats:

  • Runtime: 0 ms (100.00%)
  • Memory: 18.5 MB (88.21%)