[leetcode] 1351. Count Negative Numbers in a Sorted Matrix

[leetcode] 1351. Count Negative Numbers in a Sorted Matrix

Description

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: 8Explanation: 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.lengthn == grid[i].length1 <= m, n <= 100-100 <= grid[i][j] <= 100

分析

题目的意思是：统计一个矩阵里面所有负数的个数，因为矩阵已经是有序了，负数集中在右方和下方，所以遍历的时候倒序遍历。

代码

class Solution: def countNegatives(self, grid: List[List[int]]) -> int: m=len(grid) n=len(grid[0]) res=0 for i in range(m-1,-1,-1): for j in range(n-1,-1,-1): if(grid[i][j]<0): res+=1 else: break return res

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