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1351. Count Negative Numbers in a Sorted Matrix 👍

  • Time: $O(m + n)$
  • Space: $O(1)$
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class Solution {
 public:
  int countNegatives(vector<vector<int>>& grid) {
    const int m = grid.size();
    const int n = grid[0].size();
    int ans = 0;
    int i = m - 1;
    int j = 0;

    while (i >= 0 && j < n) {
      if (grid[i][j] < 0) {
        ans += n - j;
        --i;
      } else {
        ++j;
      }
    }

    return ans;
  }
};

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class Solution {
  public int countNegatives(int[][] grid) {
    final int m = grid.length;
    final int n = grid[0].length;
    int ans = 0;
    int i = m - 1;
    int j = 0;

    while (i >= 0 && j < n) {
      if (grid[i][j] < 0) {
        ans += n - j;
        --i;
      } else {
        ++j;
      }
    }

    return ans;
  }
}

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

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

    return ans