#include <algorithm>
#include <cassert>
#include <map>
#include <vector>

class SnapshotArray {
    int snap_id = 0;
    std::vector<std::map<int, int>> arr;

public:
    SnapshotArray(int length)
        : arr(length, std::map<int, int> { { 0, 0 } })
    {
    }

    void set(int index, int val)
    {
        arr[index][snap_id] = val;
    }

    int snap()
    {
        return snap_id++;
    }

    int get(int index, int snap_id)
    {
        auto it = std::prev(arr[index].lower_bound(snap_id + 1));
        return it == arr[index].end() ? 0 : it->second;
    }
};

/**
 * Your SnapshotArray object will be instantiated and called as such:
 * SnapshotArray* obj = new SnapshotArray(length);
 * obj->set(index,val);
 * int param_2 = obj->snap();
 * int param_3 = obj->get(index,snap_id);
 */

int main()
{
    SnapshotArray arr(3);
    arr.set(0, 5);
    assert(arr.snap() == 0);

    arr.set(0, 6);
    assert(arr.get(0, 0) == 5);
    assert(arr.get(0, 1) == 6);

    arr = SnapshotArray(1);
    arr.set(0, 15);

    assert(arr.snap() == 0);
    assert(arr.snap() == 1);
    assert(arr.snap() == 2);
    assert(arr.get(0, 2) == 15);
    assert(arr.snap() == 3);
    assert(arr.snap() == 4);
    assert(arr.get(0, 0) == 15);

    return 0;
}