2352. Equal Row and Column Pairs

Problem Link

Description

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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

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Python3

class Solution:
    def equalPairs(self, grid: List[List[int]]) -> int:
        rows, cols = len(grid), len(grid[0])
        R = defaultdict(int)
        C = defaultdict(int)
 
        for row in grid:
            h = ",".join(map(str, row))
 
            R[h] += 1
        
        for col in zip(*grid):
            h = ",".join(map(str, col))
 
            C[h] += 1
        
        res = 0
        for k, v in R.items():
            res += v * C[k]
        
        return res