Introduction

In this blog post, we will explore how to solve the LeetCode problem "946" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

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.

Explanation

Here's a solution to the problem:

• Simulate the Stack: The core idea is to simulate the push and pop operations using a stack. We iterate through the pushed array, pushing elements onto the stack.
• Match with Popped: After each push, we check if the top of the stack matches the next element to be popped from the popped array. If they match, we pop the element from the stack and advance the popped array index. We repeat this as long as the stack is not empty and the top of the stack matches the next popped element.

• Check for Empty Stack: Finally, if all elements have been successfully popped (meaning the stack is empty), it's a valid sequence, and we return True. Otherwise, it's an invalid sequence, and we return False.

• Runtime & Storage Complexity: O(N) time complexity, where N is the length of the pushed array, and O(N) space complexity due to the stack.

Code

    def validateStackSequences(pushed, popped):
    """
    Validates if the popped sequence is a possible outcome of push and pop operations on a stack.

    Args:
        pushed: A list of integers representing the push sequence.
        popped: A list of integers representing the pop sequence.

    Returns:
        True if the popped sequence is valid, False otherwise.
    """
    stack = []
    popped_index = 0

    for push_val in pushed:
        stack.append(push_val)

        while stack and stack[-1] == popped[popped_index]:
            stack.pop()
            popped_index += 1

    return not stack