1146 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 <= 5 * 104
• 0 <= index < length
• 0 <= val <= 109
• 0 <= snap_id < (the total number of times we call snap())
• At most 5 * 104 calls will be made to set, snap, and get.

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class SnapshotArray:

    def __init__(self, length: int):
        '''
        [
            [[snap_id, val_0], ...]
            [[snap_id, val_1], ...]
        ]
        '''
        self.array = [[[-1, 0]] for _ in range(length)]
        self.snap_id = 0

    def set(self, index: int, val: int) -> None:
        self.array[index].append([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:
        idx = bisect.bisect(self.array[index], [snap_id+1]) - 1
        return self.array[index][idx][1]


# 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)