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);
    }

}