## 860. 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 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:trueExplanation: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:falseExplanation: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`

.

## Rust Solution

```
struct Solution;
impl Solution {
fn lemonade_change(bills: Vec<i32>) -> bool {
let mut b5 = 0;
let mut b10 = 0;
for b in bills {
match b {
5 => {
b5 += 1;
}
10 => {
if b5 > 0 {
b10 += 1;
b5 -= 1;
} else {
return false;
}
}
20 => {
if b10 > 0 && b5 > 0 {
b10 -= 1;
b5 -= 1;
} else if b5 >= 3 {
b5 -= 3;
} else {
return false;
}
}
_ => {}
}
}
true
}
}
#[test]
fn test() {
let bills = vec![5, 5, 5, 10, 20];
assert_eq!(Solution::lemonade_change(bills), true);
let bills = vec![5, 5, 10];
assert_eq!(Solution::lemonade_change(bills), true);
let bills = vec![10, 10];
assert_eq!(Solution::lemonade_change(bills), false);
let bills = vec![5, 5, 10, 10, 20];
assert_eq!(Solution::lemonade_change(bills), false);
let bills = vec![
5, 5, 10, 20, 5, 5, 5, 5, 5, 5, 5, 5, 5, 10, 5, 5, 20, 5, 20, 5,
];
assert_eq!(Solution::lemonade_change(bills), true);
}
```

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