categories: leetcode

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题目描述

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: trueExample 3: Input: [10,10] Output: falseExample 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.

    参考代码

  1. class Solution {
  2.     public boolean lemonadeChange(int[] bills) {
  3.         if (bills[0] != 5) {//若第一个不是5，则返回false
  4.             return false;
  5.         }
  6.         else {
  7.             int five = 1,ten = 0;
  8.             int length = bills.length;
  9.             for(int i = 1;i < length;i++) {//从第二个数据开始
  10.                 if(bills[i] == 5) {
  11.                     five++;
  12.                 }
  13.                 else if(bills[i] == 10){
  14.                     if(five == 0) {
  15.                         return false;
  16.                     }
  17.                     else {//进行相应的加减
  18.                         five--;
  19.                         ten++;
  20.                     }
  22.                 }
  23.                 else {
  24.                     if(five == 0) {
  25.                         return false;
  26.                     }
  27.                     else if(ten != 0) {//10、5的情况
  28.                         five--;
  29.                         ten--;
  30.                     }
  31.                     else {
  32.                         if(five >= 3) {//5,5,5的情况
  33.                             five -= 3;
  34.                         }
  35.                         else {
  36.                             return false;
  37.                         }
  38.                     }
  39.                 }
  40.             }
  41.         }
  42.         return true;
  43.     }
  44. }

思路及总结

感觉这个题目没有体现所谓贪心算法的思想，只是一些if else的语句，以及需要考虑一些边界问题。

参考

https://www.smwenku.com/a/5bb2d3692b71770e645e1c2b/zh-cn/