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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

---

實現支持下列接口的「快照數組」-?SnapshotArray：

• SnapshotArray(int length)?- 初始化一個與指定長度相等的 類數組 的數據結構。初始時，每個元素都等于?0。
• void set(index, val)?- 會將指定索引?index?處的元素設置為?val。
• int snap()?- 獲取該數組的快照，并返回快照的編號?snap_id（快照號是調用?snap()?的總次數減去?1）。
• int get(index, snap_id)?- 根據指定的?snap_id?選擇快照，并返回該快照指定索引?index?的值。

示例：

輸入：["SnapshotArray","set","snap","set","get"][[3],[0,5],[],[0,6],[0,0]] 輸出：[null,null,0,null,5] 解釋： SnapshotArray snapshotArr = new SnapshotArray(3); // 初始化一個長度為 3 的快照數組 snapshotArr.set(0,5); // 令 array[0] = 5 snapshotArr.snap(); // 獲取快照，返回 snap_id = 0 snapshotArr.set(0,6); snapshotArr.get(0,0); // 獲取 snap_id = 0 的快照中 array[0] 的值，返回 5

提示：

• 1 <= length?<= 50000
• 題目最多進行50000?次set，snap，和?get的調用 。
• 0 <= index?<?length
• 0 <=?snap_id <?我們調用?snap()?的總次數
• 0 <=?val <= 10^9

---

480ms 1 class SnapshotArray { 2 3 private var dict = [Int: Int]() 4 private var snapshots = [[Int: Int]]() 5 6 init(_ length: Int) { 7 //array = Array(repeating: 0, count: length + 1) 8 } 9 10 func set(_ index: Int, _ val: Int) { 11 dict[index] = val 12 } 13 14 func snap() -> Int { 15 snapshots.append(dict) 16 return snapshots.count - 1 17 } 18 19 func get(_ index: Int, _ snap_id: Int) -> Int { 20 return snapshots[snap_id][index] ?? 0 21 } 22 } 23 24 /** 25 * Your SnapshotArray object will be instantiated and called as such: 26 * let obj = SnapshotArray(length) 27 * obj.set(index, val) 28 * let ret_2: Int = obj.snap() 29 * let ret_3: Int = obj.get(index, snap_id) 30 */

---

Runtime:?828 ms

Memory Usage:?27.8 MB 1 class SnapshotArray { 2 var vv:[[Int:Int]] = [[Int:Int]]() 3 4 init(_ length: Int) { 5 vv.append([Int:Int]()) 6 } 7 8 func set(_ index: Int, _ val: Int) { 9 vv[vv.count - 1][index] = val 10 } 11 12 func snap() -> Int { 13 vv.append([Int:Int]()) 14 return vv.count - 2 15 } 16 17 func get(_ index: Int, _ snap_id: Int) -> Int { 18 for i in stride(from:snap_id,through:0,by:-1) 19 { 20 if vv[i][index] != nil 21 { 22 return vv[i][index]! 23 } 24 } 25 return 0 26 } 27 } 28 29 /** 30 * Your SnapshotArray object will be instantiated and called as such: 31 * let obj = SnapshotArray(length) 32 * obj.set(index, val) 33 * let ret_2: Int = obj.snap() 34 * let ret_3: Int = obj.get(index, snap_id) 35 */

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轉載于:https://www.cnblogs.com/strengthen/p/11297779.html

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