Posted on by tzry

LeetCode 1351. Count Negative Numbers in a Sorted Matrix

Given a m * 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

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int countNegatives(int** grid, int gridSize, int* gridColSize){
    int cnt=0;
    int firstIndex = *gridColSize;
    for(int i=0;i<gridSize;++i){
        while(firstIndex>0 && grid[i][firstIndex-1]<0){
            --firstIndex;
        }
       
        if(firstIndex==0){
            cnt += *gridColSize * (gridSize-i);
            break;
        }
        else{
             cnt += *gridColSize - firstIndex;
        }
    }
    return cnt;
}


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