Leetcode 1588. 所有奇数长度子数组的和

参考：https://leetcode-cn.com/problems/sum-of-all-odd-length-subarrays/solution/cong-on3-dao-on-de-jie-fa-by-liuyubobobo/

class Solution {
     
public:
    int sumOddLengthSubarrays(vector<int>& arr) 
    {
     
        int res = 0, left_even, right_even, left_odd, right_odd;
		int size = arr.size();
        for(int i = 0; i < size; i++)
        {
     
            int left = i + 1, right = size - i;

            left_even = (left + 1) / 2;
            right_even = (right + 1) / 2;
            left_odd = left / 2;
            right_odd = right / 2;
            
            res += (left_even * right_even + left_odd * right_odd) * arr[i];
        }
        return res;
    }
};