Snapshot Array - Python Solution

 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

class SnapshotArray:

    def __init__(self, length: int):
        self.A = [{} for _ in range(length)]
        self.snap_id = 0

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

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

    def get(self, index: int, snap_id: int) -> int:
        snaps = self.A[index]
        if snap_id in snaps:
            return snaps[snap_id]
        else:
            last_val = 0
            for i in range(0,self.snap_id+1):
                if i in snaps:
                    last_val = snaps[i]
                if i >= snap_id:
                    return last_val
            return last_val


# 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)