1. Usage 用法
// "static void main" must be defined in a public class.
public class Main {
public static void main(String[] args) {
// 1. Initialize a queue.
Queue<Integer> q = new LinkedList();
// 2. Get the first element - return null if queue is empty.
System.out.println("The first element is: " + q.peek());
// 3. Push new element.
q.offer(5);
q.offer(13);
q.offer(8);
q.offer(6);
// 4. Pop an element.
q.poll();
// 5. Get the first element.
System.out.println("The first element is: " + q.peek());
// 7. Get the size of the queue.
System.out.println("The size is: " + q.size());
}
}
例 Moving Average from Data Stream
Given a stream of integers and a window size, calculate the moving average of all integers in the sliding window.
Example:
MovingAverage m = new MovingAverage(3);
m.next(1) = 1
m.next(10) = (1 + 10) / 2
m.next(3) = (1 + 10 + 3) / 3
m.next(5) = (10 + 3 + 5) / 3
class MovingAverage {
Queue<Integer> q;
double sum = 0;
int size;
public MovingAverage(int s) {
q = new LinkedList();
size = s;
}
public double next(int val) {
if(q.size() == size){
sum = sum - q.poll();
}
q.offer(val);
sum += val;
return sum/q.size();
}
}
时间复杂度 O(1)
空间复杂度 O(N)
