2681. Power of Heroes

You are given a 0-indexed integer array nums representing the strength of some heroes. The power of a group of heroes is defined as follows:

• Let i0, i1, … ,ik be the indices of the heroes in a group. Then, the power of this group is max(nums[i0], nums[i1], ... ,nums[ik])2 * min(nums[i0], nums[i1], ... ,nums[ik]).

Return the sum of the power of all non-empty groups of heroes possible. Since the sum could be very large, return it modulo 109 + 7.

class Solution {
public:
    int sumOfPower(vector<int>& nums) {
        sort(begin(nums), end(nums));
        long long res = 0, mod = 1e9 + 7, sum = 0;
        for(int i = 0; i < nums.size(); i++) {
            long long ma = 1ll * nums[i] * nums[i] % mod;
            if(i >= 2) sum = (sum + nums[i-2]) % mod * 2 % mod;
            long long x = (sum + nums[i] + (i ? nums[i-1] : 0)) % mod;
            res = (res + ma * x % mod) % mod;
        }
        return res;
    }
};