# ---
# title: 1146. Snapshot Array
# id: problem1146
# author: Tian Jun
# date: 2020-10-31
# difficulty: Medium
# categories: Array
# link: <https://leetcode.com/problems/snapshot-array/description/>
# hidden: true
# ---
# 
# 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`
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
