1582. Special Positions in a Binary Matrix
Difficulty: Easy
Related Topics: Array
Given a rows x cols
matrix mat
, where mat[i][j]
is either 0
or 1
, return the number of special positions in mat
.
A position (i,j)
is called special if mat[i][j] == 1
and all other elements in row i
and column j
are 0
(rows and columns are 0-indexed).
Example 1:
Input: mat = [[1,0,0],
[0,0,1],
[1,0,0]]
Output: 1
Explanation: (1,2) is a special position because mat[1][2] == 1 and all other elements in row 1 and column 2 are 0.
Example 2:
Input: mat = [[1,0,0],
[0,1,0],
[0,0,1]]
Output: 3
Explanation: (0,0), (1,1) and (2,2) are special positions.
Example 3:
Input: mat = [[0,0,0,1],
[1,0,0,0],
[0,1,1,0],
[0,0,0,0]]
Output: 2
Example 4:
Input: mat = [[0,0,0,0,0],
[1,0,0,0,0],
[0,1,0,0,0],
[0,0,1,0,0],
[0,0,0,1,1]]
Output: 3
Constraints:
rows == mat.length
cols == mat[i].length
1 <= rows, cols <= 100
mat[i][j]
is0
or1
.
Solution
Language: Python3
class Solution:
def numSpecial(self, mat: List[List[int]]) -> int:
row=set()
for r in range(len(mat)):
if sum(mat[r])==1:
row.add(r)
rep=0
for c in range(len(mat[0])):
tmp=[]
for r in range(len(mat)):
if mat[r][c]==1:
tmp.append(r)
if len(tmp)==1 and tmp[0] in row:
rep+=1
return rep