Snapshot Array

class SnapshotArray {
    
    private Map<Integer, Map<Integer, Integer>> map;
    private int snapId;

    public SnapshotArray(int length) {
        this.map = new HashMap<>();
        this.snapId = 0;
        map.put(snapId, new HashMap<>());
    }
    
    public void set(int index, int val) {
        map.get(snapId).put(index, val);
    }
    
    public int snap() {
        map.put(++snapId, new HashMap<>());
        return snapId - 1;
    }
    
    public int get(int index, int snapId) {
        while(snapId >= 0) {
            if(map.get(snapId).containsKey(index)) {
                return map.get(snapId).get(index);
            }
            snapId--;
        }
        return 0;
    }
}

/**
 * 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);
 */