Valid-Stack-Sequences-O(n).java

class Solution {
    public boolean validateStackSequences(int[] pushed, int[] popped) {
        Stack<Integer> st = new Stack<>();
        int j = 0;

        for(int val: pushed){
            st.push(val);
            while(!st.isEmpty() && st.peek() == popped[j]){
                j++;
                st.pop();
            }
        }

        return st.isEmpty();
    }
}