[Swift]LeetCode860. 柠檬水找零 | Lemonade Change

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➤微信公众号：山青咏芝（shanqingyongzhi）
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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.

---

在柠檬水摊上，每一杯柠檬水的售价为 5 美元。

顾客排队购买你的产品，（按账单 bills 支付的顺序）一次购买一杯。

每位顾客只买一杯柠檬水，然后向你付 5 美元、10美元或 20 美元。你必须给每个顾客正确找零，也就是说净交易是每位顾客向你支付 5 美元。

注意，一开始你手头没有任何零钱。

如果你能给每位顾客正确找零，返回 true ，否则返回 false 。

示例 1：

输入：[5,5,5,10,20]
输出：true
解释：
前 3 位顾客那里，我们按顺序收取 3 张 5 美元的钞票。
第 4 位顾客那里，我们收取一张 10 美元的钞票，并返还 5 美元。
第 5 位顾客那里，我们找还一张 10 美元的钞票和一张 5 美元的钞票。
由于所有客户都得到了正确的找零，所以我们输出 true。

示例 2：

输入：[5,5,10]
输出：true

示例 3：

输入：[10,10]
输出：false

示例 4：

输入：[5,5,10,10,20]
输出：false
解释：
前 2 位顾客那里，我们按顺序收取 2 张 5 美元的钞票。
对于接下来的 2 位顾客，我们收取一张 10 美元的钞票，然后返还 5 美元。
对于最后一位顾客，我们无法退回 15 美元，因为我们现在只有两张 10 美元的钞票。
由于不是每位顾客都得到了正确的找零，所以答案是 false。

提示：

• 0 <= bills.length <= 10000
• bills[i] 不是 5 就是 10 或是 20 

---

Runtime: 104 ms

Memory Usage: 19 MB

class Solution {
    func lemonadeChange(_ bills: [Int]) -> Bool {        
        var fiveLeft = 0 
        var tenLeft = 0
        var twentyLeft = 0
        for i in 0..<bills.count {
            if bills[i] == 5 {
                fiveLeft += 1
            } else if bills[i] == 10 {
                tenLeft += 1
                fiveLeft -= 1
            } else {
                twentyLeft += 1
                if tenLeft > 0 {
                    tenLeft -= 1
                    fiveLeft -= 1
                } else {
                    fiveLeft -= 3
                }                
            }
            
            if fiveLeft < 0 || tenLeft < 0 {
                return false
            }            
        }
        
        return true        
    }
}

---

104ms

class Solution {
    func lemonadeChange(_ bills: [Int]) -> Bool {
        if bills.count == 0 {
            return true
        }
        
        var fiveDollarBills = 0
        var tenDollarBills = 0
        
        for bill in bills {
            if bill == 5 {
                fiveDollarBills += 1
            } else if bill == 10 {
                if fiveDollarBills == 0 {
                    return false
                }
                fiveDollarBills -= 1
                tenDollarBills += 1
            } else if bill == 20 {
                if tenDollarBills > 0 && fiveDollarBills > 0 {
                    tenDollarBills -= 1
                    fiveDollarBills -= 1
                } else if fiveDollarBills > 2 {
                    fiveDollarBills -= 3
                } else {
                    return false
                }
            }
        }
        
        return true
    }
}

---

108ms

class Solution {
    func lemonadeChange(_ bills: [Int]) -> Bool {        
        var fiveLeft = 0 
        var tenLeft = 0
        var twentyLeft = 0
        for i in 0..<bills.count {
            if bills[i] == 5 {
                fiveLeft += 1
            } else if bills[i] == 10 {
                tenLeft += 1
                fiveLeft -= 1
            } else {
                twentyLeft += 1
                if tenLeft > 0 {
                    tenLeft -= 1
                    fiveLeft -= 1
                } else {
                    fiveLeft -= 3
                }                
            }            
            if fiveLeft < 0 {
                return false
            }            
        }        
        return true        
    }
}

---

108ms

class Solution {
    func lemonadeChange(_ bills: [Int]) -> Bool {
        var c5 = 0
        var c10 = 0

        for i in bills {
            if i == 5{
                c5 += 1
            }
            else if i == 10{
                if c5 > 0{
                    c5 -= 1
                    c10 += 1
                }else{
                    return false
                }
            }else {
                if c5 > 0 && c10 > 0{
                    c5 -= 1
                    c10 -= 1
                }else if c5 > 3{
                    c5 -= 3
                }else{
                    return false
                }
            }
        }
        return true
    }
}

---

110ms

class Solution {
   func lemonadeChange(_ bills: [Int]) -> Bool {
       
        var dic = [Int:Int]()
        dic.updateValue(0, forKey: 5)
        dic.updateValue(0, forKey: 10)
        dic.updateValue(0, forKey: 20)
        for i  in 0..<bills.count {
            if bills[i] - 5 == 0{
                dic.updateValue(dic[5]! + 1, forKey: 5)
                continue
            }
            let dif = bills[i] - 5
            let tenCount =  dif/10
            let fiveCount =  dif/5
            let sfiveCount =  fiveCount - tenCount * 2
            var needFive: Int = 0
            
            if dic[10]! - tenCount < 0{
                 needFive = (tenCount - dic[10]!) * 2
            }
            if dic[5]! < needFive  + sfiveCount{
                return false
            }else{
               dic.updateValue(max(0, dic[5]! - needFive - sfiveCount), forKey: 5)
            }
            dic.updateValue(max(0, dic[10]! - tenCount), forKey: 10)
            dic.updateValue(dic[bills[i]]!  + 1, forKey: bills[i])
        }
       return true
    }
}

---

112ms

class Solution {
    func lemonadeChange(_ bills: [Int]) -> Bool {
        var fiveSum = 0, tenSum = 0, twentySum = 0
        let five = 5, ten = 10, twenty = 20
        
        for bill in bills {
            switch bill {
            case five:
                fiveSum += bill
            case ten:
                if fiveSum > 0 {
                    fiveSum -= five
                    tenSum += bill
                } else {
                    return false
                }
            case twenty:
                if tenSum > 0 {
                    if fiveSum > 0 {
                        tenSum -= ten
                        fiveSum -= five
                    } else {
                        return false
                    }
                } else if fiveSum >= five * 3 {
                    fiveSum -= five * 3
                } else {
                    return false
                }
                
                twentySum += bill
            default: break
            }
        }
        
        return true
    }
}

---

120ms

class Solution {
    func lemonadeChange(_ bills: [Int]) -> Bool {
        var bank = [5:0, 10:0]
        for bill in bills {
            if bill == 5 {
                bank[5]! += 1
            }

            if bill == 10 {
                if bank[5]! == 0 {
                    return false
                } else {
                    bank[5]! -= 1
                    bank[10]! += 1
                }
            }

            if bill == 20 {
                if bank[10]! > 0 && bank[5]! > 0 {
                    bank[10]! -= 1
                    bank[5]! -= 1
                } else if bank[5]! >= 3 {
                    bank[5]! -= 3
                } else {
                    return false
                }
            }
        }
        return true
    }
}