Lemonade change

/*
 * At a lemonade stand, each lemonade costs $5. Customers are standing in a queue to buy from you and order one at a time (in the order specified by bills). Each customer will only buy one lemonade and pay with either a $5, $10, or $20 bill. You must provide the correct change to each customer so that the net transaction is that the customer pays $5.
 * Note that you do not have any change in hand at first.
 * Given an integer array bills where bills[i] is the bill the ith customer pays, return true if you can provide every customer with the correct change, or false otherwise.
 * Example 1:
 * Input: bills = [5,5,5,10,20]
 * Output: true
 * Explanation:
 * From the first 3 customers, we collect three $5 bills in order.
 * From the fourth customer, we collect a $10 bill and give back a $5.
 * From the fifth customer, we give a $10 bill and a $5 bill.
 * Since all customers got correct change, we output true.
 * Example 2:
 * Input: bills = [5,5,10,10,20]
 * Output: false
 * Explanation:
 * From the first two customers in order, we collect two $5 bills.
 * For the next two customers in order, we collect a $10 bill and give back a $5 bill.
 * For the last customer, we can not give the change of $15 back because we only have two $10 bills.
 * Since not every customer received the correct change, the answer is false.
 * Constraints:
 * 1 <= bills.length <= 105
 * bills[i] is either 5, 10, or 20.
 */

impl Solution {
  pub fn lemonade_change(bills: Vec<i32>) -> bool {
    let mut fives = 0i32;
    let mut tens = 0i32;
    for bill in bills {
      match bill {
        5 => fives += 1,
        10 => {
          if fives == 0 { return false; }
          fives -= 1;
          tens += 1;
        }
        20 => {
          if tens > 0 && fives > 0 {
            tens -= 1;
            fives -= 1;
          } else if fives >= 3 {
            fives -= 3;
          } else {
            return false;
          }
        }
        _ => {}
      }
    }
    true
  }
}