# 946. Validate Stack Sequences

Validate Stack Sequences - LeetCode

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.
``````

• code
``````class Solution:
def validateStackSequences(self, pushed: List[int], popped: List[int]) -> bool:
stack = []
i = 0
for v in pushed:
stack.append(v)
# check if we need to pop popped(move index instead)
while stack and i < len(popped) and popped[i] == stack[-1]:
stack.pop()
i += 1
return i == len(popped) # not stack
``````