leetcode - 2352. Equal Row and Column Pairs

Description

Given a 0-indexed n x n integer matrix grid, return the number of pairs (ri, cj) such that row ri and column cj are equal.

A row and column pair is considered equal if they contain the same elements in the same order (i.e., an equal array).

Example 1:

Input: grid = [[3,2,1],[1,7,6],[2,7,7]]
Output: 1
Explanation: There is 1 equal row and column pair:
- (Row 2, Column 1): [2,7,7]

Example 2:

Input: grid = [[3,1,2,2],[1,4,4,5],[2,4,2,2],[2,4,2,2]]
Output: 3
Explanation: There are 3 equal row and column pairs:
- (Row 0, Column 0): [3,1,2,2]
- (Row 2, Column 2): [2,4,2,2]
- (Row 3, Column 2): [2,4,2,2]

Constraints:

n == grid.length == grid[i].length
1 <= n <= 200
1 <= grid[i][j] <= 10^5

Solution

Iterate the whole table, every time check if the current row is the same as current column, in other words, compare the matrix and the transposed matrix.

Time complexity: $o(n^3)$
Space complexity: $o(1)$

Code

class Solution:
    def equalPairs(self, grid: List[List[int]]) -> int:
        grid_transpose = list(zip(*grid))
        n = len(grid)
        cnt = 0
        for i in range(n):
            for j in range(n):
                if tuple(grid[i]) == grid_transpose[j]:
                    cnt += 1
        return cnt