#1146

Snapshot Array

medium · 36.7% accepted · 3,915 likes · top 14%

array · hash table · binary search · design

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Description

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

Solution