# Leetcode: Validate Stack Sequences

Validate Stack Sequences

Similar Problems:

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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

• Solution:
```// Blog link: https://code.dennyzhang.com/validate-stack-sequences
// Basic Ideas: two pointers + stack
// Complexity: Time O(n), Space O(n)
func validateStackSequences(pushed []int, popped []int) bool {
stack := []int{}
j := 0
for _, v := range pushed {
stack = append(stack, v)
for len(stack) > 0 && stack[len(stack)-1] == popped[j] {
stack = stack[0:len(stack)-1]
j++
}
}
return len(stack) == 0
}
```

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