Java

  • /**
    
     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 don't have any change in hand at first.
    
     Return true if and only if you can provide every customer with correct change.
    
    
    
     Example 1:
    
     Input: [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: [5,5,10]
     Output: true
    
    
     Example 3:
    
     Input: [10,10]
     Output: false
    
    
     Example 4:
    
     Input: [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't give change of $15 back because we only have two $10 bills.
     Since not every customer received correct change, the answer is false.
    
    
     Note:
    
     0 <= bills.length <= 10000
     bills[i] will be either 5, 10, or 20.
    
     */
    
    public class Lemonade_Change {
    
        class Solution {
    
            int count5 = 0;
            int count10 = 0;
            int count20 = 0;
    
            public boolean lemonadeChange(int[] bills) {
    
                if (bills == null || bills.length == 0) {
                    return false;
                }
    
                for (int i = 0; i < bills.length; i++) {
    
                    if (bills[i] == 5) {
                        count5++;
                    } else if (bills[i] == 10) {
                        if (count5 > 0) {
                            count5--;
                            count10++;
                        } else {
                            return false;
                        }
                    } else if (bills[i] == 20) {
                        if (count5 > 0 && count10 > 0) {
                            count5--;
                            count10--;
                            count20++; // not used, but still record it
                        } else if (count5 > 2) {
                            count5 -= 3;
                        } else {
                            return false;
                        }
                    }
                }
    
                return true;
            }
        }
    }
    
  • // OJ: https://leetcode.com/problems/lemonade-change/
    // Time: O(N)
    // Space: O(1)
    class Solution {
    public:
        bool lemonadeChange(vector<int>& bills) {
            int five = 0, ten = 0;
            for (auto b : bills) {
                if (b == 5) {
                    ++five;
                } else if (b == 10) {
                    if (!five) return false;
                    --five;
                    ++ten;
                } else {
                    if (five && ten) {
                        --five;
                        --ten;
                    } else if (five >= 3) {
                        five -= 3;
                    } else {
                        return false;
                    }
                }
            }
            return true;
        }
    };
    
  • class Solution:
        def lemonadeChange(self, bills):
            """
            :type bills: List[int]
            :rtype: bool
            """
            changes = {5:0, 10:0}
            for bill in bills:
                if bill == 5:
                    changes[5] += 1
                elif bill == 10:
                    if changes[5] == 0:
                        return False
                    else:
                        changes[10] += 1
                        changes[5] -= 1
                elif bill == 20:
                    if changes[10] != 0:
                        if changes[5] == 0:
                            return False
                        else:
                            changes[5] -= 1
                            changes[10] -= 1
                    else:
                        if changes[5] < 3:
                            return False
                        else:
                            changes[5] -= 3
            return True
    

Java

  • class Solution {
        public boolean lemonadeChange(int[] bills) {
            int count5 = 0, count10 = 0;
            int length = bills.length;
            for (int i = 0; i < length; i++) {
                int bill = bills[i];
                if (bill == 5)
                    count5++;
                else if (bill == 10) {
                    count10++;
                    if (count5 == 0)
                        return false;
                    else
                        count5--;
                } else if (bill == 20) {
                    if (count10 == 0) {
                        if (count5 < 3)
                            return false;
                        else
                            count5 -= 3;
                    } else {
                        if (count5 == 0)
                            return false;
                        else {
                            count10--;
                            count5--;
                        }
                    }
                }
            }
            return true;
        }
    }
    
  • // OJ: https://leetcode.com/problems/lemonade-change/
    // Time: O(N)
    // Space: O(1)
    class Solution {
    public:
        bool lemonadeChange(vector<int>& bills) {
            int five = 0, ten = 0;
            for (auto b : bills) {
                if (b == 5) {
                    ++five;
                } else if (b == 10) {
                    if (!five) return false;
                    --five;
                    ++ten;
                } else {
                    if (five && ten) {
                        --five;
                        --ten;
                    } else if (five >= 3) {
                        five -= 3;
                    } else {
                        return false;
                    }
                }
            }
            return true;
        }
    };
    
  • class Solution:
        def lemonadeChange(self, bills):
            """
            :type bills: List[int]
            :rtype: bool
            """
            changes = {5:0, 10:0}
            for bill in bills:
                if bill == 5:
                    changes[5] += 1
                elif bill == 10:
                    if changes[5] == 0:
                        return False
                    else:
                        changes[10] += 1
                        changes[5] -= 1
                elif bill == 20:
                    if changes[10] != 0:
                        if changes[5] == 0:
                            return False
                        else:
                            changes[5] -= 1
                            changes[10] -= 1
                    else:
                        if changes[5] < 3:
                            return False
                        else:
                            changes[5] -= 3
            return True
    

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