1561. Maximum Number of Coins You Can Get

There are 3n piles of coins of varying size, you and your friends will take piles of coins as follows:

• In each step, you will choose any 3 piles of coins (not necessarily consecutive).
• Of your choice, Alice will pick the pile with the maximum number of coins.
• You will pick the next pile with the maximum number of coins.
• Your friend Bob will pick the last pile.
• Repeat until there are no more piles of coins.

Given an array of integers piles where piles[i] is the number of coins in the ith pile.

Return the maximum number of coins that you can have.

class Solution {
public:
    int maxCoins(vector<int>& piles) {
        int res = 0, pick = piles.size() / 3;
        sort(begin(piles), end(piles));
        for(int i = piles.size() - 2; pick; i -= 2, pick -= 1)
            res += piles[i];
        return res;
    }
};