[Swift]LeetCode946. 驗證棧序列 | Validate Stack Sequences

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Given two sequences pushed and popped with distinct values, return true if and only if this could have been the result of a sequence of push and pop operations on an initially empty stack.

 Example 1:

Input: pushed = [1,2,3,4,5], popped = [4,5,3,2,1] Output: true Explanation: We might do the following sequence: push(1), push(2), push(3), push(4), pop() -> 4, push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1 

Example 2:

Input: pushed = [1,2,3,4,5], popped = [4,3,5,1,2] Output: false Explanation: 1 cannot be popped before 2. 

 Note:

1. 0 <= pushed.length == popped.length <= 1000
2. 0 <= pushed[i], popped[i] < 1000
3. pushed is a permutation of popped.
4. pushed and popped have distinct values.

---

給定 pushed 和 popped 兩個序列，只有當它們多是在最初空棧上進行的推入 push 和彈出 pop 操做序列的結果時，返回 true；不然，返回 false 。

示例 1：

輸入：pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
輸出：true
解釋：咱們能夠按如下順序執行：
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1

示例 2：

輸入：pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
輸出：false
解釋：1 不能在 2 以前彈出。

 提示：

1. 0 <= pushed.length == popped.length <= 1000
2. 0 <= pushed[i], popped[i] < 1000
3. pushed 是 popped 的排列。

---

64ms

 1 class Solution {
 2     func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
 3        var i = 0;
 4         
 5         var result = [Int]()
 6         for element in pushed {
 7             result.append(element)
 8             
 9             while !result.isEmpty && result.last! == popped[i] {
10                 result.removeLast()
11                 i += 1
12             }
13         }
14         
15         return result.count == 0 ? true : false
16     }
17 }

---

68ms

 1 class Solution {
 2     func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
 3         var pop = popped
 4         var stack: [Int] = []
 5         var pushCount = pushed.count
 6         var i = 0
 7         while !pop.isEmpty && i < pushCount {
 8             stack.append(pushed[i])
 9             i += 1
10             while let first = pop.first, let last = stack.last, first == last {
11                 pop.remove(at: 0)
12                 stack.remove(at: stack.count - 1)   
13             }
14         }
15         return pop.count == 0
16         
17     }
18 }

---

72ms

 1 class Solution {
 2     func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
 3         var s:Stack<Int> = Stack<Int>()
 4         var j:Int = 0
 5         for i in 0..<pushed.count
 6         {
 7             s.push(pushed[i])
 8             while (!s.isEmpty() && j < popped.count && s.getLast() == popped[j])
 9             {
10                 s.pop()
11                 j += 1
12             }
13         }
14         return s.isEmpty() && j == popped.count
15     }
16 }
17 
18 public struct Stack<T> {
19     
20     // 泛型數組：用於存儲數據元素
21     fileprivate var stack: [T] 
22 
23     // 返回堆棧中元素的個數
24     public var count: Int {
25         return stack.count
26     }
27     
28     /// 構造函數：建立一個空的堆棧
29     public init() {
30         stack = [T]()
31     }
32     
33     // 檢查堆棧是否爲空
34     // - returns: 若是堆棧爲空，則返回true，不然返回false
35     public func isEmpty() -> Bool {
36         return stack.isEmpty
37     }
38     
39     // 入堆棧操做：將元素添加到堆棧的末尾
40     public mutating func push(_ element: T) {
41         stack.append(element)
42     }
43     
44     // 出堆棧操做：刪除並返回堆棧中的第一個元素
45     public mutating func pop() -> T? {
46         return stack.removeLast()
47     }
48  
49     // 返回堆棧中的第一個元素(不刪除)
50     public func getLast() -> T? {
51         return stack.last!
52     }
53 }

---

72ms

 1 class Solution {
 2     func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
 3         var push = pushed
 4         var pop = popped
 5         var qs = [Int]()
 6         while let u = pop.first {
 7             if let v = qs.last, v == u {
 8                 qs.removeLast()
 9                 pop.remove(at: 0)
10                 continue
11             }
12             if let v = push.first, v == u {
13                 push.remove(at: 0)
14                 pop.remove(at: 0)
15                 continue
16             }
17             guard !push.isEmpty else {
18                 return false
19             }
20             let r = push.remove(at: 0)
21             qs.append(r)
22         }
23         guard push.isEmpty, pop.isEmpty else {
24             return false
25         }
26         return true
27     }
28 }

---

80ms

 1 class Solution {
 2     func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
 3         var popped = popped
 4         var stack = [Int]()
 5         for item in pushed {
 6             stack.append(item)
 7             while stack.last == popped.first && popped.first != nil {
 8                 stack.removeLast()
 9                 popped.removeFirst()
10             }
11         }
12         while stack.last == popped.first && popped.first != nil {
13             stack.removeLast()
14             popped.removeFirst()
15         }
16         return stack.isEmpty
17     }
18 }

---

92ms

 1 class Solution {
 2     func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
 3         var currentStack: [Int] = []
 4         var nextPushIndex = 0
 5         var nextPopIndex = 0
 6         
 7         while nextPopIndex < popped.count {
 8             let poppedValue = popped[nextPopIndex]
 9             
10             while currentStack.last != poppedValue && nextPushIndex < pushed.count {
11                 currentStack.append(pushed[nextPushIndex])
12                 nextPushIndex += 1
13             }
14             
15             if currentStack[currentStack.count - 1] != poppedValue {
16                 return false
17             } else {
18                 currentStack.removeLast()
19             }
20             
21             nextPopIndex += 1
22         }
23         
24         return true
25     }
26 }

---

100ms

 1 class Solution {
 2     func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
 3         guard pushed.count == popped.count else { return false }
 4         var st: [Int] = []
 5         
 6         var pushIt = 0
 7         var popIt = 0
 8         
 9         while pushIt < pushed.count {
10             st.append(pushed[pushIt])
11             //print(st, pushIt, popIt)
12             while st.count > 0 && st[st.count - 1] == popped[popIt] {
13                 //print("del ", st, pushIt, popIt)
14                 st.remove(at: st.count - 1)
15                 popIt += 1
16             }
17             pushIt += 1
18         }
19         
20         return st.count == 0
21     }
22 }

---

104ms

 1 class Solution {
 2     func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
 3         if (pushed.count != popped.count) {
 4             return false
 5         } 
 6         
 7         var stack = [Int]()        
 8         var N = pushed.count
 9         var j = 0
10         
11         
12         for x in pushed {
13             stack.append(x)
14             while(stack.count > 0 && 
15                   j < N && 
16                   stack.last == popped[j]) {
17                 stack.popLast()
18                 j += 1
19             }
20         }        
21         
22         return j == N
23     }
24 }