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Formatted question description: https://leetcode.ca/all/1561.html

# 1561. Maximum Number of Coins You Can Get (Medium)

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 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 which 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 <= 10^5
• piles.length % 3 == 0
• 1 <= piles[i] <= 10^4

Related Topics:
Sort

## Solution 1.

// OJ: https://leetcode.com/problems/maximum-number-of-coins-you-can-get/
// Time: O(NlogN)
// Space: O(1)
class Solution {
public:
int maxCoins(vector<int>& A) {
sort(begin(A), end(A));
int i = 0, j = A.size() - 1, ans = 0;
while (i < j) {
++i;
--j;
ans += A[j--];
}
return ans;
}
};


## Solution 2.

// OJ: https://leetcode.com/problems/maximum-number-of-coins-you-can-get/
// Time: O(NlogN)
// Space: O(1)
class Solution {
public:
int maxCoins(vector<int>& A) {
sort(begin(A), end(A));
int N = A.size(), ans = 0;
for (int i = N / 3; i < N; i += 2) ans += A[i];
return ans;
}
};


Java

• class Solution {
public int maxCoins(int[] piles) {
Arrays.sort(piles);
int length = piles.length;
int rounds = length / 3;
int maxCoins = 0;
int index = length - 2;
for (int i = 0; i < rounds; i++) {
maxCoins += piles[index];
index -= 2;
}
return maxCoins;
}
}

• // OJ: https://leetcode.com/problems/maximum-number-of-coins-you-can-get/
// Time: O(NlogN)
// Space: O(1)
class Solution {
public:
int maxCoins(vector<int>& A) {
sort(begin(A), end(A));
int i = 0, j = A.size() - 1, ans = 0;
while (i < j) {
++i;
--j;
ans += A[j--];
}
return ans;
}
};

• class Solution:
def maxCoins(self, piles: List[int]) -> int:
piles.sort()
return sum(piles[-2 : len(piles) // 3 - 1 : -2])