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Java-based LeetCode algorithm problem solutions, regularly updated

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package g2301_2400.s2352_equal_row_and_column_pairs;

// #Medium #Array #Hash_Table #Matrix #Simulation
// #2022_08_07_Time_7_ms_(98.94%)_Space_71.4_MB_(27.97%)

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

/**
 * 2352 - Equal Row and Column Pairs\.
 *
 * Medium
 *
 * Given a **0-indexed** `n x n` integer matrix `grid`, _return the number of pairs_ (R_i, C_j) _such that row_ R_i _and column_ C_j _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:**
 *
 * ![](https://assets.leetcode.com/uploads/2022/06/01/ex1.jpg)
 *
 * **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:**
 *
 * ![](https://assets.leetcode.com/uploads/2022/06/01/ex2.jpg)
 *
 * **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
**/
public class Solution {
    public int equalPairs(int[][] grid) {
        int[] tmpCol = new int[grid.length];
        Map pairsMap = new HashMap<>();
        int pairsCounter = 0;
        for (int col = 0; col < grid[0].length; col++) {
            for (int row = 0; row < grid.length; row++) {
                tmpCol[row] = grid[row][col];
            }
            int hashCode = Arrays.hashCode(tmpCol);
            pairsMap.put(hashCode, pairsMap.getOrDefault(hashCode, 0) + 1);
        }
        for (int[] row : grid) {
            int hashCode = Arrays.hashCode(row);
            if (pairsMap.containsKey(hashCode)) {
                pairsCounter += pairsMap.get(hashCode);
            }
        }
        return pairsCounter;
    }
}