add: 220504 [cpp]

cpp/2205/220504.cpp

@@ -0,0 +1,28 @@
+#include <vector>
+#include <unordered_map>
+
+/**
+ * 1679. Max Number of K-Sum Pairs
+ * You are given an integer array nums and an integer k.
+ * In one operation, you can pick two numbers from the array whose sum equals k and remove them from the array.
+ * Return the maximum number of operations you can perform on the array.
+ */
+
+class Solution {
+public:
+	static int maxOperations(const std::vector<int>& nums, int k) {
+		std::unordered_map<int, int> m;
+		for (int i : nums)
+			++m[i];
+		int ret = (k & 1) ? 0 : (m[k / 2] / 2);
+		const int pivot = (k & 1) ? (k / 2 + 1) : (k / 2);
+		for (const auto& [idx, cnt] : m)
+			if (idx < pivot && m.count(k - idx))
+				ret += std::min(m[idx], m[k - idx]);
+		return ret;
+	}
+};
+
+int main() {
+	Solution::maxOperations({2,2,2,3,1,1,4,1}, 4);
+}

cpp/2205/CMakeLists.txt

@@ -3,4 +3,4 @@ PROJECT(2205)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2204 220504-CN.cpp)
+ADD_EXECUTABLE(2204 220504.cpp)