LeetCode860.Lemonade Change

LeetCode860.Lemonade Change

题目

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.

思路

分类讨论。

代码

class Solution {
public:
    bool lemonadeChange(vector<int>& bills) {
        int i, j, k, ans = 0;
        int a[25];
        a[5] = 0;
        a[10] = 0;
        a[20] = 0;
        for(i=0; i<bills.size(); i++) {
            j = bills[i] - 5;
            if(j > ans) {
                return false;
            }
            if(j == 0) {
                ans = ans + 5;
                a[5]++;
                continue;
            }
            if(j == 5) {
                if(a[5] == 0) {
                    return false;
                }
                else {
                    a[5]--;
                    a[10]++;
                    ans+=5;
                    continue;
                }
            }
            if(a[10]) {
                if(a[5]==0) {
                    return false;
                }
                a[10]--;
                a[5]--;
                a[20]++;
                ans = ans+=5;
            }
            else {
                if(a[5] <= 2) {
                    return false;
                }
                a[5] = a[5] - 3;
                ans = ans+=5;
            }
        }
        return true;
    }
};