[Swift]LeetCode1146. 快照數組 | Snapshot Array

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?微信公眾號：山青詠芝（shanqingyongzhi）
?博客園地址：山青詠芝（https://www.cnblogs.com/strengthen/）
?GitHub地址：https://github.com/strengthen/LeetCode
?原文地址：https://www.cnblogs.com/strengthen/p/11297779.html?
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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

class SnapshotArray {

    private var dict = [Int: Int]()
    private var snapshots = [[Int: Int]]()
    
    init(_ length: Int) {
        //array = Array(repeating: 0, count: length + 1)
    }
    
    func set(_ index: Int, _ val: Int) {
        dict[index] = val
    }
    
    func snap() -> Int {
        snapshots.append(dict)
        return snapshots.count - 1
    }
    
    func get(_ index: Int, _ snap_id: Int) -> Int {
        return snapshots[snap_id][index] ?? 0
    }
}

/**
 * Your SnapshotArray object will be instantiated and called as such:
 * let obj = SnapshotArray(length)
 * obj.set(index, val)
 * let ret_2: Int = obj.snap()
 * let ret_3: Int = obj.get(index, snap_id)
 */

---

Runtime:?828 ms

Memory Usage:?27.8 MB

class SnapshotArray {
    var vv:[[Int:Int]] = [[Int:Int]]()

    init(_ length: Int) {
        vv.append([Int:Int]())        
    }
    
    func set(_ index: Int, _ val: Int) {
        vv[vv.count - 1][index] = val
    }
    
    func snap() -> Int {
        vv.append([Int:Int]()) 
        return vv.count - 2
    }
    
    func get(_ index: Int, _ snap_id: Int) -> Int {
        for i in stride(from:snap_id,through:0,by:-1)
        {
            if vv[i][index] != nil
            {
                return vv[i][index]!
            }
        }
        return 0
    }
}

/**
 * Your SnapshotArray object will be instantiated and called as such:
 * let obj = SnapshotArray(length)
 * obj.set(index, val)
 * let ret_2: Int = obj.snap()
 * let ret_3: Int = obj.get(index, snap_id)
 */

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