🟡 Port problem 1497 (Check If Array Pairs Are Divisible by k) from Python to C++23

solutions/1401-1500/1497-check-if-array-pairs-are-divisible-by-k/README.md

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+# 1497. Check If Array Pairs Are Divisible by k
+
+[LeetCode problem 1497](https://leetcode.com/problems/check-if-array-pairs-are-divisible-by-k/)
+
+- **Difficulty**: Medium
+- **Tags**: array, hash-table, counting
+
+## Description
+
+Given an array of integers `arr` of even length `n` and an integer `k`,
+determine whether it's possible to divide the array into exactly `n / 2`
+pairs such that the sum of each pair is divisible by `k`.

solutions/1401-1500/1497-check-if-array-pairs-are-divisible-by-k/solution.cpp

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+#include "solution.hpp"
+
+namespace leetcode::p1497 {
+
+bool solve(const std::vector<int>& arr, int k) {
+    std::vector<int> remainderCounts(static_cast<std::size_t>(k), 0);
+
+    for (int value : arr) {
+        int remainder = ((value % k) + k) % k;
+        ++remainderCounts[static_cast<std::size_t>(remainder)];
+    }
+
+    if (remainderCounts[0] % 2 != 0) {
+        return false;
+    }
+
+    for (int remainder = 1; remainder <= k / 2; ++remainder) {
+        if (remainderCounts[static_cast<std::size_t>(remainder)] !=
+            remainderCounts[static_cast<std::size_t>(k - remainder)]) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+} // namespace leetcode::p1497

solutions/1401-1500/1497-check-if-array-pairs-are-divisible-by-k/solution.hpp

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+#pragma once
+
+#include <vector>
+
+namespace leetcode::p1497 {
+
+// optimized: O(n + k) time, O(k) space — count remainders mod k, then check
+// that each remainder's count matches its complement's (k - r) count.
+bool solve(const std::vector<int>& arr, int k);
+
+} // namespace leetcode::p1497

solutions/1401-1500/1497-check-if-array-pairs-are-divisible-by-k/test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include "solution.hpp"
+
+TEST_CASE("Problem 1497", "[p1497]") {
+    CHECK(leetcode::p1497::solve({1, 2, 3, 4, 5, 10, 6, 7, 8, 9}, 5));
+    CHECK(leetcode::p1497::solve({1, 2, 3, 4, 5, 6}, 7));
+    CHECK_FALSE(leetcode::p1497::solve({1, 2, 3, 4, 5, 6}, 10));
+    CHECK(leetcode::p1497::solve({-1, 1, -2, 2, -3, 3, -4, 4}, 3));
+}