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 given index to be equal to val.
• int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1.
• int get(index, snap_id) returns the value at the given index, at the time we took the snapshot with the given snap_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 to set, snap, and get.
• 0 <= index < length
• 0 <= snap_id < (the total number of times we call snap())
• 0 <= val <= 10^9

SOLUTION:

class SnapshotArray:

    def __init__(self, length: int):
        self.snaps = {}
        self.sid = 0
        self.n = length

    def set(self, index: int, val: int) -> None:
        self.snaps[(self.sid, index)] = val

    def snap(self) -> int:
        res = self.sid
        self.sid += 1
        return res

    def getSnap(self, snap_id, index):
        for i in range(snap_id, -1, -1):
            if (i, index) in self.snaps:
                return self.snaps[(i, index)]
        return 0

    def get(self, index: int, snap_id: int) -> int:
        return self.getSnap(snap_id, index)

# Your SnapshotArray object will be instantiated and called as such:
# obj = SnapshotArray(length)
# obj.set(index,val)
# param_2 = obj.snap()
# param_3 = obj.get(index,snap_id)