LeetCode: Equal Row and Column Pairs

Find the number of equal row and column pairs in a square matrix using Python.

For this solution, I created two hash maps to track the frequency of each row and column in the grid.

I converted each row and column into a tuple, since lists are not hashable and cannot be used as dictionary keys.

Next, I find the intersection of the keys in both hash maps to identify the rows and columns that are identical.

Finally, for each identical row-column pair, I multiply their frequencies from both hash maps and sum these products to get the total count of equal row and column pairs.

class Solution:
    def equalPairs(self, grid: List[List[int]]) -> int:
        n = len(grid)
        seen_cols = {}
        seen_rows = {}

        for i in range(n):
            col = tuple(grid[i])
            seen_cols[col] = seen_cols.get(col, 0) + 1

            row = tuple([grid[j][i] for j in range(n)])
            seen_rows[row] = seen_rows.get(row, 0) + 1

        seen_both = seen_cols.keys() & seen_rows.keys()

        total_count = 0
        for x in seen_both:
            total_count += seen_cols[x] * seen_rows[x]

        return int(total_count)