2144. Minimum Cost of Buying Candies With Discount

We have to get the items with a maximum discount to get the minimum cost we have to pay.

For example if we have:

input: cost = [3, 7, 1, 5, 9, 11, 15]

We know that the maximum discount we can get is 9 because we can buy two candies with costs 11 and 15.

Now let us sort cost in non-increasing order. Using this, we can get the maximum discounts we can get throughout:

cost = [15, 11, 9, 7, 5, 3, 1]

We can start with the first elements 15, 11, 9. We can buy candies 15 and 11, and get a discount of 9.

Then we have elements 7, 5, 3. We can buy elements 7, and 5 to get a discount of 3.

Then we have to buy 1.

So basically, if we sort nums in non-increasing order and then if an element is the third element, we know it is the discount element.

func minimumCost(cost []int) int {
    sort.Slice(cost, func(i, j int) bool { return cost[i] > cost[j] })
    res := 0
    
    for i := 0; i < len(cost); i++ {
        if (i + 1) % 3 == 0 {
            continue
        }
        res += cost[i]
    }
    
    return res
}