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2352. Equal Row and Column Pairs

Difficulty Topics

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] <= 105

Solution

equal-row-and-column-pairs.py
class Solution:
    def equalPairs(self, grid: List[List[int]]) -> int:
        rows, cols = len(grid), len(grid[0])
        R = Counter()
        C = Counter()

        for row in grid:
            R[tuple(row)] += 1

        for col in zip(*grid):
            C[tuple(col)] += 1

        res = 0
        for row, cnt in R.items():
            res += cnt * C[row]

        return res