Window Sum

Given an array of n integers, and a moving window(size k), move the window at each iteration from the start of the array, find the sum of the element inside the window at each moving.

Example

Example 1

Input：array = [1,2,7,8,5], k = 3
Output：[10,17,20]
Explanation：
1 + 2 + 7 = 10
2 + 7 + 8 = 17
7 + 8 + 5 = 20

思路：滑动窗口，sum + A[j] , 然后减去sum - A[i]; 分count < k，和count == k两种情况；

public class Solution {
    /**
     * @param nums: a list of integers.
     * @param k: length of window.
     * @return: the sum of the element inside the window at each moving.
     */
    public int[] winSum(int[] nums, int k) {
        if(nums == null || nums.length == 0 || k <= 0) {
            return new int[0];
        }
        int n = nums.length;
        int[] res = new int[n-k+1];
        int i = 0; int j = 0;
        int count = 0;
        int sum = 0;
        int index = 0;
        while(j < n) {
            if(count < k) {
                sum += nums[j++];
                count++;
            } 
            if(count == k) {
                res[index++] = sum;
                sum -= nums[i++];
                count--;
            }
        }
        return res;
    }
}