Minimum cost of buying candies with discount

Array Greedy Sorting

62.7% acceptance

Feb 25, 2026

688

A shop is selling candies at a discount. For every two candies sold, the shop gives a third candy for free. The customer can choose any candy to take away for free as long as the cost of the chosen candy is less than or equal to the minimum cost of the two candies bought. Given a 0-indexed integer array cost, where cost[i] denotes the cost of the ith candy, return the minimum cost of buying all the candies.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn minimum_cost(cost: Vec<i32>) -> i32 {
    let mut cost = cost;
    cost.sort_unstable_by(|a, b| b.cmp(a)); // descending
    // Every 3rd item (index 2, 5, 8, ...) is free
    cost.iter()
      .enumerate()
      .filter(|(i, _)| (i + 1) % 3 != 0)
      .map(|(_, &c)| c)
      .sum()
  }
}