Maximum Number of Coins You Can Get

Description

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.

Example 1:

Input: piles = [2,4,1,2,7,8] Output: 9 Explanation: Choose the triplet (2, 7, 8), Alice Pick the pile with 8 coins, you the pile with 7 coins and Bob the last one. Choose the triplet (1, 2, 4), Alice Pick the pile with 4 coins, you the pile with 2 coins and Bob the last one. The maximum number of coins which you can have are: 7 + 2 = 9. On the other hand if we choose this arrangement (1, 2, 8), (2, 4, 7) you only get 2 + 4 = 6 coins which is not optimal.

Example 2:

Input: piles = [2,4,5] Output: 4

Example 3:

Input: piles = [9,8,7,6,5,1,2,3,4] Output: 18

Constraints:

• 3 <= piles.length <= 105
• piles.length % 3 == 0
• 1 <= piles[i] <= 104

Code

Time Complexity: $O(n\log n)$, Space Complexity: $O(1)$

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

Source

• Maximum Number of Coins You Can Get - LeetCode