README.md

2352. Equal Row and Column Pairs

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

Solutions (Rust)

1. Solution

use std::collections::HashMap;

impl Solution {
    pub fn equal_pairs(grid: Vec<Vec<i32>>) -> i32 {
        let mut count = HashMap::new();
        let mut ret = 0;

        for i in 0..grid.len() {
            count
                .entry(grid[i].clone())
                .and_modify(|c| *c += 1)
                .or_insert(1);
        }

        for i in 0..grid.len() {
            let col = (0..grid.len()).map(|j| grid[j][i]).collect::<Vec<_>>();

            ret += count.get(&col).unwrap_or(&0);
        }

        ret
    }
}