[Swift]LeetCode946. 验证栈序列 | 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.

---

给定 pushed 和 popped 两个序列，只有当它们可能是在最初空栈上进行的推入 push 和弹出 pop 操作序列的结果时，返回 true；否则，返回 false 。

示例 1：

输入：pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
输出：true
解释：我们可以按以下顺序执行：
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1

示例 2：

输入：pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
输出：false
解释：1 不能在 2 之前弹出。

 提示：

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

---

64ms

class Solution {
    func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
       var i = 0;
        
        var result = [Int]()
        for element in pushed {
            result.append(element)
            
            while !result.isEmpty && result.last! == popped[i] {
                result.removeLast()
                i += 1
            }
        }
        
        return result.count == 0 ? true : false
    }
}

---

68ms

class Solution {
    func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
        var pop = popped
        var stack: [Int] = []
        var pushCount = pushed.count
        var i = 0
        while !pop.isEmpty && i < pushCount {
            stack.append(pushed[i])
            i += 1
            while let first = pop.first, let last = stack.last, first == last {
                pop.remove(at: 0)
                stack.remove(at: stack.count - 1)   
            }
        }
        return pop.count == 0
        
    }
}

---

72ms

class Solution {
    func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
        var s:Stack<Int> = Stack<Int>()
        var j:Int = 0
        for i in 0..<pushed.count
        {
            s.push(pushed[i])
            while (!s.isEmpty() && j < popped.count && s.getLast() == popped[j])
            {
                s.pop()
                j += 1
            }
        }
        return s.isEmpty() && j == popped.count
    }
}

public struct Stack<T> {
    
    // 泛型数组：用于存储数据元素
    fileprivate var stack: [T] 

    // 返回堆栈中元素的个数
    public var count: Int {
        return stack.count
    }
    
    /// 构造函数：创建一个空的堆栈
    public init() {
        stack = [T]()
    }
    
    // 检查堆栈是否为空
    // - returns: 如果堆栈为空，则返回true，否则返回false
    public func isEmpty() -> Bool {
        return stack.isEmpty
    }
    
    // 入堆栈操作：将元素添加到堆栈的末尾
    public mutating func push(_ element: T) {
        stack.append(element)
    }
    
    // 出堆栈操作：删除并返回堆栈中的第一个元素
    public mutating func pop() -> T? {
        return stack.removeLast()
    }
 
    // 返回堆栈中的第一个元素(不删除)
    public func getLast() -> T? {
        return stack.last!
    }
}

---

72ms

class Solution {
    func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
        var push = pushed
        var pop = popped
        var qs = [Int]()
        while let u = pop.first {
            if let v = qs.last, v == u {
                qs.removeLast()
                pop.remove(at: 0)
                continue
            }
            if let v = push.first, v == u {
                push.remove(at: 0)
                pop.remove(at: 0)
                continue
            }
            guard !push.isEmpty else {
                return false
            }
            let r = push.remove(at: 0)
            qs.append(r)
        }
        guard push.isEmpty, pop.isEmpty else {
            return false
        }
        return true
    }
}

---

80ms

class Solution {
    func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
        var popped = popped
        var stack = [Int]()
        for item in pushed {
            stack.append(item)
            while stack.last == popped.first && popped.first != nil {
                stack.removeLast()
                popped.removeFirst()
            }
        }
        while stack.last == popped.first && popped.first != nil {
            stack.removeLast()
            popped.removeFirst()
        }
        return stack.isEmpty
    }
}

---

92ms

class Solution {
    func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
        var currentStack: [Int] = []
        var nextPushIndex = 0
        var nextPopIndex = 0
        
        while nextPopIndex < popped.count {
            let poppedValue = popped[nextPopIndex]
            
            while currentStack.last != poppedValue && nextPushIndex < pushed.count {
                currentStack.append(pushed[nextPushIndex])
                nextPushIndex += 1
            }
            
            if currentStack[currentStack.count - 1] != poppedValue {
                return false
            } else {
                currentStack.removeLast()
            }
            
            nextPopIndex += 1
        }
        
        return true
    }
}

---

100ms

class Solution {
    func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
        guard pushed.count == popped.count else { return false }
        var st: [Int] = []
        
        var pushIt = 0
        var popIt = 0
        
        while pushIt < pushed.count {
            st.append(pushed[pushIt])
            //print(st, pushIt, popIt)
            while st.count > 0 && st[st.count - 1] == popped[popIt] {
                //print("del ", st, pushIt, popIt)
                st.remove(at: st.count - 1)
                popIt += 1
            }
            pushIt += 1
        }
        
        return st.count == 0
    }
}

---

104ms

class Solution {
    func validateStackSequences(_ pushed: [Int], _ popped: [Int]) -> Bool {
        if (pushed.count != popped.count) {
            return false
        } 
        
        var stack = [Int]()        
        var N = pushed.count
        var j = 0
        
        
        for x in pushed {
            stack.append(x)
            while(stack.count > 0 && 
                  j < N && 
                  stack.last == popped[j]) {
                stack.popLast()
                j += 1
            }
        }        
        
        return j == N
    }
}