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thewitchking

Jul 7th, 2025

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#include <iostream>
#include <list>
#include <unordered_map>
class VideoHistory {
private:
std::list<int> history; // Doubly linked list to maintain order
std::unordered_map<int, std::list<int>::iterator> videoMap; // Map to access list nodes in O(1)
const size_t maxSize = 3;
public:
void watchVideo(int videoId) {
// If video is already in history, remove it from its current position
if (videoMap.find(videoId) != videoMap.end()) {
history.erase(videoMap[videoId]);
} else if (history.size() == maxSize) {
// Remove the least recently used (last element)
int lastVideo = history.back();
videoMap.erase(lastVideo);
history.pop_back();
}
// Add new video to the front (most recent)
history.push_front(videoId);
videoMap[videoId] = history.begin();
}
void printHistory() const {
std::cout << "Video History (most recent first): ";
for (int id : history) {
std::cout << id << " ";
}
std::cout << std::endl;
}
};
int main() {
VideoHistory vh;
vh.watchVideo(101);
vh.watchVideo(102);
vh.watchVideo(103);
vh.printHistory(); // Output: 103 102 101
vh.watchVideo(103);
vh.printHistory(); // Output: 103 102 101 (103 moved to front, order same due to re-watch)
vh.watchVideo(104);
vh.printHistory(); // Output: 104 103 102 (101 evicted)
vh.watchVideo(102);
vh.printHistory(); // Output: 102 104 103
return 0;
}

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