Snapshot Array
Implement a SnapshotArray that supports the following interface:
SnapshotArray(int length)
initializes an array-like data structure with the given length. Initially, each element equals 0.void set(index, val)
sets the element at the givenindex
to be equal toval
.int snap()
takes a snapshot of the array and returns thesnap_id
: the total number of times we calledsnap()
minus1
.int get(index, snap_id)
returns the value at the givenindex
, at the time we took the snapshot with the givensnap_id
Example 1:
Input: ["SnapshotArray","set","snap","set","get"]
[[3],[0,5],[],[0,6],[0,0]]
Output: [null,null,0,null,5]
Explanation:
SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3
snapshotArr.set(0,5); // Set array[0] = 5
snapshotArr.snap(); // Take a snapshot, return snap_id = 0
snapshotArr.set(0,6);
snapshotArr.get(0,0); // Get the value of array[0] with snap_id = 0, return 5
Constraints:
1 <= length <= 50000
At most
50000
calls will be made toset
,snap
, andget
.0 <= index < length
0 <= snap_id <
(the total number of times we callsnap()
)0 <= val <= 10^9
// We are only adding data for the values that change over a snap
// TreeMap -> floorKey(id) & ceilingKey(id)
class SnapshotArray {
// Arrays of maps, where map are between snap_id -> element
TreeMap<Integer, Integer>[] array;
int snap_id;
// O(NlogN)
public SnapshotArray(int length) {
this.snap_id = 0;
array = new TreeMap[length];
for (int i = 0; i < length; i++) {
array[i] = new TreeMap<>();
array[i].put(0, 0);
}
}
// O(logN)
public void set(int index, int val) {
array[index].put(this.snap_id, val);
}
// O(1)
public int snap() {
int snapped = snap_id;
this.snap_id++;
return snapped;
}
// O(logN)
public int get(int index, int id) {
// We will get that value from the snap_id <= id
// Which ever is available
Integer lastSnapID = array[index].floorKey(id);
return array[index].get(lastSnapID);
}
}
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