Today I have done leetcode's August LeetCoding Challenge with cpp.

August LeetCoding Challenge 15

Description

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.

Solution

class Solution {
public:
  bool lemonadeChange(vector<int>& bills) {
    int five = 0;
    int ten = 0;
    for(auto b : bills) {
      if(b == 5) {
        five += 1;
      } else if(b == 10) {
        if(!five) return false;
        ten += 1;
        five -= 1;
      } else if(b == 20) {
        if(five && ten) {
          five -= 1;
          ten -= 1;
        } else if(five > 2) {
          five -= 3;
        } else {
          return false;
        }
      }
    }
    return true;
  }
};