3427. Sum of Variable Length Subarrays

You are given an integer array nums of size n. For each index i where 0 <= i < n, define a subarray nums[start ... i] where start = max(0, i - nums[i]).

Return the total sum of all elements from the subarray defined for each index in the array.

class Solution {
public:
    int subarraySum(vector<int>& nums) {
        int res = 0;
        for(int i = 0; i < nums.size(); i++) {
            for(int j = max(0, i - nums[i]); j <= i; j++) res += nums[j];
        }
        return res;
    }
};