LeetCode 1685. 有序数组中差绝对值之和（前缀和）

示例 1：
输入：nums = [2,3,5]
输出：[4,3,5]
解释：假设数组下标从 0 开始，那么
result[0] = |2-2| + |2-3| + |2-5| = 0 + 1 + 3 = 4，
result[1] = |3-2| + |3-3| + |3-5| = 1 + 0 + 2 = 3，
result[2] = |5-2| + |5-3| + |5-5| = 3 + 2 + 0 = 5。

示例 2：
输入：nums = [1,4,6,8,10]
输出：[24,15,13,15,21]
 
提示：
2 <= nums.length <= 10^5
1 <= nums[i] <= nums[i + 1] <= 10^4

class Solution {
public:
    vector<int> getSumAbsoluteDifferences(vector<int>& nums) {
        int n = nums.size();
        vector<int> sum(1+n, 0), ans(n);
        for(int i = 1; i <= n; ++i) 
        {
            sum[i] = nums[i-1]+sum[i-1];//前缀和
        }
        
        for(int i = 1; i <= n; ++i)
        {
            int presum = sum[i-1];
            int tailsum = sum[n]-sum[i];
            ans[i-1] = (i-1)*nums[i-1]-presum+tailsum-(n-i)*nums[i-1];
        }
        return ans;
    }
};