# 946. Validate Stack Sequences

Medium
Given two integer arrays `pushed` and `popped` each with distinct values, return `true` if this could have been the result of a sequence of push and pop operations on an initially empty stack, or `false` otherwise.
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.
Constraints:
• `1 <= pushed.length <= 1000`
• `0 <= pushed[i] <= 1000`
• All the elements of `pushed` are unique.
• `popped.length == pushed.length`
• `popped` is a permutation of `pushed`.

### 解題

func validateStackSequences(pushed []int, popped []int) bool {
stack := make([]int, 0)
i := 0
for _, n := range pushed {
stack = append(stack, n) // 先把值 push 進去
// 檢查 stack 最後一個是不是目前要 pop 的
// 可以的話就持續 pop
for len(stack) != 0 && stack[len(stack)-1] == popped[i] {
stack = stack[:len(stack)-1]
i++
}
}
return len(stack) == 0 // stack 被 pop 完了，代表可行
}