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Snapshot Array in Python
Suppose we have to Implement a SnapshotArray that supports the following interfaces −
SnapshotArray(int length) this will initialize the array-like data structure with the given length. Initially, each element equals 0.
set(index, val) this will sets the element at the given index to be equal to val.
snap() will take a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1.
get(index, snap_id) this will return the value at the given index, at the time we took the snapshot with the given snap_id
So if the array size is 2, it is set using [0, 5], after that we take a snap, it will return 0, then set using [0, 6], and get(0, 0), this will return 5.
To solve this, we will follow these steps −
The initialize method will be like −
current := 0
arr := an array of length + 1 number of 2d arrays [[0, 0]]
The set() method will be like −
temp := last element of arr[index]
if temp[0] = current, then element of index 1 from the last element of arr[index] := val
otherwise insert [current, val] into arr[index]
The snap() method will be like−
increase current by 1, return one less than count
The get() method will be like −
temp := arr[index], low := 0, high := length of temp – 1
while low < high
mid := low + (high – low) / 2
if temp[mid, 0] <= snap_id, then low := mid, otherwise high := mid – 1
return temp[low, 1]
Example(Python)
Let us see the following implementation to get better understanding −
class SnapshotArray(object): def __init__(self, length): self.current = 0 self.arr = [[[0,0]] for i in range(length+1)] def set(self, index, val): temp = self.arr[index][-1] #print(temp) if temp[0] == self.current: self.arr[index][-1][1] = val else: self.arr[index].append([self.current,val]) def snap(self): self.current+=1 return self.current -1 def get(self, index, snap_id): temp = self.arr[index] low = 0 high = len(temp)-1 while low < high: mid = low + (high - low+1 )//2 if temp[mid][0]<=snap_id: low = mid else: high = mid -1 return temp[low][1] ob = SnapshotArray(3) ob.set(0,5) print(ob.snap()) ob.set(0,6) print(ob.get(0,0))
Input
Initialize the array using 3, then call set(0,5), snap(), set(0,6), get(0, 0)
Output
0 5
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