LESSON 38 / 75·2 min readIntermediate

Stack and queue in Java

Should knowConcept lesson

01 Understand02 Recall 03 Prepare

Stack

Use Deque<Integer> stack = new ArrayDeque<>();

Queue

Use Queue<Integer> queue = new LinkedList<>();

Problems to practice

Valid Parentheses
Min Stack
Daily Temperatures
Largest Rectangle in Histogram
Sliding Window Maximum
Implement Queue using Stacks

Example: stack-based validation

Deque<Character> stack = new ArrayDeque<>();
for (char ch : s.toCharArray()) {
    if (ch == '(' || ch == '{' || ch == '[') {
        stack.push(ch);
    } else if (!stack.isEmpty() && isMatching(stack.peek(), ch)) {
        stack.pop();
    } else {
        return false;
    }
}
return stack.isEmpty();

PAUSE & RECALL