1146. 快照数组.cpp

class SnapshotArray {
public:

   
    
  unordered_map<int, map<int, int>> a;
int cur_snap = 0;
SnapshotArray(int length) {}
int snap() { return cur_snap++; }
void set(int index, int val) { 
  a[index][cur_snap] = val; 
}
int get(int index, int snap_id) {
  auto it = a[index].upper_bound(snap_id);
  return it == begin(a[index]) ? 0 : prev(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);
 */