860. Lemonade Change

 I recently solved the "Lemonade Change" problem on LeetCode and wanted to share my approach. This problem requires us to determine if we can provide correct change to each customer in a queue, given they may pay with $5, $10, or $20 bills, while the price of lemonade is always $5.

Problem Summary:

  • Objective: Ensure each customer receives the correct change.
  • Constraints: You can only provide change with the bills you have received from previous customers.

Approach:

I used a greedy algorithm to solve this problem, focusing on always giving change in the largest denominations first to maximize the availability of smaller bills for future transactions.

Code Explanation: (javascript)

/**
 * @param {number[]} bills
 * @return {boolean}
 */
var lemonadeChange = function(bills) {
    let count5 = 0;
    let count10 = 0;
    for(let i = 0; i < bills.length; i++){
        if(bills[i] == 5){
            count5++;
        }else if(bills[i] == 10){
            count5--;
            count10++;
        }else{
            if(count10 >= 1){
                count10--;
                count5--;
            }else{
                count5 -= 3;
            }
        }
        if(count5 < 0){
            return false;
        }
    }
    return true;
};

Code Explanation:(java)

class Solution {
    public boolean lemonadeChange(int[] bills) {
       int count5 = 0;
       int count10 = 0;
       for(int i = 0; i < bills.length; i++){
           if(bills[i] == 5){
               count5++;
            }else if(bills[i] == 10){
               count5--;
               count10++;
            }else{
                if(count10 >= 1){
                count10--;
                count5--;
            }else{
                count5 -= 3;
            }
        }
        if(count5 < 0){
            return false;
        }
    }
    return true;
    }
}

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