add: 220425-CN [cpp]

cpp/2204/220425-CN.cpp

@@ -0,0 +1,31 @@
+#include <vector>
+#include <random>
+#include <ctime>
+#include <unordered_map>
+
+/**
+ * 398. Random Pick Index
+ * Given an integer array nums with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array.
+ * Implement the Solution class:
+ * Solution(int[] nums) Initializes the object with the array nums.
+ * int pick(int target) Picks a random index i from nums where nums[i] == target. If there are multiple valid i's, then each index should have an equal probability of returning.
+ */
+
+class Solution {
+private:
+	std::unordered_map<int, std::vector<int>> m;
+
+	std::mt19937 r;
+
+public:
+	explicit Solution(const std::vector<int>& nums) : r(std::time(nullptr)) {
+		auto x = nums.size();
+		while (x--) {
+			m[nums[x]].push_back(x);
+		}
+	}
+
+	int pick(int target) {
+		return m[target][r() % m[target].size()];
+	}
+};

cpp/2204/CMakeLists.txt

@@ -3,4 +3,4 @@ PROJECT(2204)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2204 220425.cpp)
+ADD_EXECUTABLE(2204 220425-CN.cpp)