# 13.06.2023 [2352. Equal Row and Column Pairs]

Count of `rowArray` == `colArray` in an `n x n` matrix.

13.06.2023

2352. Equal Row and Column Pairs medium
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https://t.me/leetcode_daily_unstoppable/244

Problem TLDR

Count of rowArray == colArray in an n x n matrix.

Intuition

Compute hash function for each row and each col, then compare them. If hash(row) == hash(col), then compare arrays.
For hashing, we can use simple 31 * prev + curr, that encodes both value and position.

Approach

• For this Leetcode data, tan hash works perfectly, we can skip comparing the arrays.

Complexity

• Time complexity:
  O(n^2)

• Space complexity:
  O(n)

Code

fun equalPairs(grid: Array<IntArray>): Int {
    val rowHashes = grid.map { it.fold(0.0) { r, t ->  Math.tan(r) + t } }
    val colHashes = (0..grid.lastIndex).map { x ->
        (0..grid.lastIndex).fold(0.0) { r, t -> Math.tan(r) + grid[t][x] } }
        return (0..grid.size * grid.size - 1).count {
            rowHashes[it / grid.size] == colHashes[it % grid.size]
        }
    }