LeetCode 946: Validate Stack Sequences Solution

Master LeetCode problem 946 (Validate Stack Sequences), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

946. Validate Stack Sequences

Medium

Array Stack Simulation

Problem Explanation

Explanation

We can simulate the process of pushing and popping elements onto a stack based on the given pushed and popped arrays. We iterate through the pushed array, pushing elements onto a stack one by one. After pushing each element, we check if the top element of the stack is the same as the next element to be popped. If they match, we pop the element from the stack. Finally, if the stack is empty after processing all elements, we return true; otherwise, we return false.

Algorithm:

Initialize an empty stack.
Iterate through the pushed array:
- Push the element onto the stack.
- While the stack is not empty and the top element of the stack is equal to the next element to be popped:
  - Pop the element from the stack.
If the stack is empty after processing all elements, return true; otherwise, return false.

Time Complexity: O(n) where n is the number of elements in the pushed array. We iterate through each element once.

Space Complexity: O(n) where n is the number of elements in the pushed array. We use a stack to store elements.

Solution Code

class Solution {
    public boolean validateStackSequences(int[] pushed, int[] popped) {
        Stack<Integer> stack = new Stack<>();
        int i = 0;
        for (int num : pushed) {
            stack.push(num);
            while (!stack.isEmpty() && i < popped.length && stack.peek() == popped[i]) {
                stack.pop();
                i++;
            }
        }
        return stack.isEmpty();
    }
}

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