Equal row and column pairs

Array Hash Table Matrix Simulation

70.8% acceptance

Feb 25, 2026

2484

192

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).

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

use std::collections::HashMap;


impl Solution {
  pub fn equal_pairs(grid: Vec<Vec<i32>>) -> i32 {
    let n = grid.len();
    let mut row_count: HashMap<Vec<i32>, i32> = HashMap::new();
    for row in &grid {
      *row_count.entry(row.clone()).or_insert(0) += 1;
    }
    let mut ans = 0;
    for j in 0..n {
      let col: Vec<i32> = (0..n).map(|i| grid[i][j]).collect();
      ans += *row_count.get(&col).unwrap_or(&0);
    }
    ans
  }
}