G面经prepare: Data Stream Average

给一个datastream和一个fixed window size, 让我design一个class可以完成add number还有find average in the window. 就是不能用vector得用array. 

当然用queue是最好的

package DataStreamAverage;

import java.util.*;

public class Solution {
    int count;
    int sum;
    Queue<Integer> q;

    public Solution() {
        this.count = 0;
        this.sum = 0;
        this.q = new LinkedList<Integer>();
    }

    public ArrayList<Double> average (HashSet<Integer> set, int L) {
        ArrayList<Double> result = new ArrayList<Double>();
        Iterator<Integer> iter = set.iterator();
        while (iter.hasNext()) {
            int cur = iter.next();
            q.offer(cur);
            count++;
            sum += cur;
            if (q.size()>L) {
                int front = q.peek();
                sum -= front;
                count--;
                q.poll();
            }
            double aver = (double)sum/count;
            result.add(aver);
        }
        return result;

    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        HashSet<Integer> set = new HashSet<Integer>();
        for (int i=1; i<=10; i++) {
            set.add(i);
        }
        Solution sol = new Solution();
        ArrayList<Double> res = sol.average(set, 2);
        System.out.println(res);
    }

}

当然用fixed size array也可以，但是要小心，一个是要折回，二个是要删除数组元素之前存在的数

 package DataStreamAverage;

 import java.util.*;

 public class Solution2 {
     int count;
     int sum;
     int[] arr;
     int pos;

     public Solution2(int size) {
         this.count = 0;
         this.sum = 0;
         this.arr = new int[size];
         Arrays.fill(arr, Integer.MIN_VALUE);
         this.pos = 0;
     }

     public ArrayList<Double> average (HashSet<Integer> set, int L) {
         ArrayList<Double> result = new ArrayList<Double>();
         Iterator<Integer> iter = set.iterator();
         while (iter.hasNext()) {
             int cur = iter.next();
             if (pos == arr.length) {
                 pos = 0;
             }
             if (arr[pos] != Integer.MIN_VALUE) {
                 sum -= arr[pos];
                 count--;
             }
             arr[pos] = cur;
             sum += arr[pos];
             pos++;
             count++;
             double aver = (double)sum/count;
             result.add(aver);
         }
         return result;
     }

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         HashSet<Integer> set = new HashSet<Integer>();
         for (int i=1; i<=10; i++) {
             set.add(i);
         }
         Solution2 sol = new Solution2(2);
         ArrayList<Double> res = sol.average(set, 2);
         System.out.println(res);
     }

 }