[LintCode] Problem 604 - Window Sum

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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

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

Code

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public int[] winSum(int[] nums, int k) {
    if (nums == null || k <= 0 || nums.length < k)
        return new int[0];
        
    int n = nums.length;
    int[] result = new int[n-k+1];
    int sum = 0;

    for (int i = 0; i < k; i++)
        result[0] += nums[i];

    for (int i = 1; i < n - k + 1; i++)
        result[i] = result[i-1] - nums[i-1] + nums[i+k-1];
        
    return result;
}