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.
Solutions
Solution 1: Stack Simulation
We iterate through the $\textit{pushed}$ array. For the current element $x$ being iterated, we push it into the stack $\textit{stk}$. Then, we check if the top element of the stack is equal to the next element to be popped in the $\textit{popped}$ array. If they are equal, we pop the top element from the stack and increment the index $i$ of the next element to be popped in the $\textit{popped}$ array. Finally, if all elements can be popped in the order specified by the $\textit{popped}$ array, return $\textit{true}$; otherwise, return $\textit{false}$.
The time complexity is $O(n)$, and the space complexity is $O(n)$. Here, $n$ is the length of the $\textit{pushed}$ array.