##### Welcome to Subscribe On Youtube
• /**

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.

Note:

0 <= bills.length <= 10000
bills[i] will be either 5, 10, or 20.

*/

class Solution {

int count5 = 0;
int count10 = 0;
int count20 = 0;

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;
}
}
}

############

class Solution {
int five = 0, ten = 0;
for (int v : bills) {
if (v == 5) {
++five;
} else if (v == 10) {
++ten;
--five;
} else {
if (ten > 0) {
--ten;
--five;
} else {
five -= 3;
}
}
if (five < 0) {
return false;
}
}
return true;
}
}

• // OJ: https://leetcode.com/problems/lemonade-change/
// Time: O(N)
// Space: O(1)
class Solution {
public:
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: List[int]) -> bool:
five = ten = 0
for v in bills:
if v == 5:
five += 1
elif v == 10:
ten += 1
five -= 1
else:
if ten:
ten -= 1
five -= 1
else:
five -= 3
if five < 0:
return False
return True

############
3
class Solution:
"""
: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

• func lemonadeChange(bills []int) bool {
five, ten := 0, 0
for _, v := range bills {
if v == 5 {
five++
} else if v == 10 {
ten++
five--
} else {
if ten > 0 {
ten--
five--
} else {
five -= 3
}
}
if five < 0 {
return false
}
}
return true
}

• function lemonadeChange(bills: number[]): boolean {
let five = 0;
let ten = 0;
for (let bill of bills) {
switch (bill) {
case 5:
five++;
break;
case 10:
five--;
ten++;
break;
case 20:
if (ten !== 0) {
ten -= 1;
bill -= 10;
}
five -= bill / 5 - 1;
break;
}

if (five < 0) {
return false;
}
}
return true;
}


• impl Solution {
pub fn lemonade_change(bills: Vec<i32>) -> bool {
let (mut five, mut ten) = (0, 0);
for bill in bills.iter() {
match bill {
5 => {
five += 1;
}
10 => {
five -= 1;
ten += 1;
}
_ => {
if ten != 0 {
ten -= 1;
five -= 1;
} else {
five -= 3;
}
}
}

if five < 0 {
return false;
}
}
true
}
}


• class Solution {
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;
}
}

############

class Solution {
int five = 0, ten = 0;
for (int v : bills) {
if (v == 5) {
++five;
} else if (v == 10) {
++ten;
--five;
} else {
if (ten > 0) {
--ten;
--five;
} else {
five -= 3;
}
}
if (five < 0) {
return false;
}
}
return true;
}
}

• // OJ: https://leetcode.com/problems/lemonade-change/
// Time: O(N)
// Space: O(1)
class Solution {
public:
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: List[int]) -> bool:
five = ten = 0
for v in bills:
if v == 5:
five += 1
elif v == 10:
ten += 1
five -= 1
else:
if ten:
ten -= 1
five -= 1
else:
five -= 3
if five < 0:
return False
return True

############
3
class Solution:
"""
: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

• func lemonadeChange(bills []int) bool {
five, ten := 0, 0
for _, v := range bills {
if v == 5 {
five++
} else if v == 10 {
ten++
five--
} else {
if ten > 0 {
ten--
five--
} else {
five -= 3
}
}
if five < 0 {
return false
}
}
return true
}

• function lemonadeChange(bills: number[]): boolean {
let five = 0;
let ten = 0;
for (let bill of bills) {
switch (bill) {
case 5:
five++;
break;
case 10:
five--;
ten++;
break;
case 20:
if (ten !== 0) {
ten -= 1;
bill -= 10;
}
five -= bill / 5 - 1;
break;
}

if (five < 0) {
return false;
}
}
return true;
}


• impl Solution {
pub fn lemonade_change(bills: Vec<i32>) -> bool {
let (mut five, mut ten) = (0, 0);
for bill in bills.iter() {
match bill {
5 => {
five += 1;
}
10 => {
five -= 1;
ten += 1;
}
_ => {
if ten != 0 {
ten -= 1;
five -= 1;
} else {
five -= 3;
}
}
}

if five < 0 {
return false;
}
}
true
}
}