贪心算法：

例如：当你去卖柠檬水 5块钱一杯

你一开始没有零钱

你需要给每位顾客合理的找钱

这时候要判断能不能找钱就需用贪心算法

程序如下：

s = [5]
a = [0,0,0]
true = 1
for i in range(len(s)):
    if s[0] != 5:
        print(False)
        true = 0
        break
    elif s[i] == 5:
        a[0] = a[0] + 1
    elif s[i] == 10:
        if a[0] >= 1:
            a[1] = a[1] + 1
            a[0] = a[0] - 1
        else:
            print(False)
            true = 0
            break
    elif s[i] == 20:
        if a[0] >= 1 and a[1] >= 1:
            a[2] = a[2] + 1
            a[1] = a[1] - 1
            a[0] = a[0] - 1
        elif a[0] >= 3:
            a[2] = a[2] + 1
            a[0] = a[0] - 3
        else:
            print(False)
            true = 0
            break
if true == 1:
    print("true")