#include <unordered_map>
#include <queue>
#include <vector>

/*
    The number container system can do the following:

    1. insert or replace a number at the given index 
    2. return the smallest index for the given number in the system

*/

class NumberContainers {
private:
    std::unordered_map<int, int> nums;
    std::unordered_map<int, std::priority_queue<int, std::vector<int>, std::greater<int>>> heap;
public:
    NumberContainers() = default;

    void change(int index, int number) {
        nums[index] = number;
        heap[number].push(index);
    }

    int find(int number) {
        while (!heap[number].empty() && nums[heap[number].top()] != number) {
            heap[number].pop();
        }

        if (heap[number].empty()) {
            return -1;
        }
        return heap[number].top();
    }
};