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 <= 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`

1146. Snapshot Array
``````type Pair = (usize, i32);

struct SnapshotArray {
size: usize,
data: Vec<Vec<Pair>>,
snap_id: usize,
}

impl SnapshotArray {
fn new(length: i32) -> Self {
let size = length as usize;
let data = vec![vec![(0, 0)]; size];
let snap_id = 0;
SnapshotArray {
size,
data,
snap_id,
}
}

fn set(&mut self, index: i32, val: i32) {
let i = index as usize;
if let Some(last) = self.data[i].pop() {
if last.0 != self.snap_id {
self.data[i].push(last);
}
}
self.data[i].push((self.snap_id, val));
}

fn snap(&mut self) -> i32 {
self.snap_id += 1;
(self.snap_id - 1) as i32
}

fn get(&self, index: i32, snap_id: i32) -> i32 {
let i = index as usize;
let snap_id = snap_id as usize;
match self.data[i].binary_search_by_key(&snap_id, |p| p.0) {
Ok(j) => self.data[i][j].1,
Err(j) => self.data[i][j - 1].1,
}
}
}

#[test]
fn test() {
let mut obj = SnapshotArray::new(3);
obj.set(0, 5);
assert_eq!(obj.snap(), 0);
obj.set(0, 6);
assert_eq!(obj.get(0, 0), 5);
}
``````