PAT-adavanced-python-1002 A+B for Polynomials

1002 A+B for Polynomials (25 分)
This time, you are supposed to find A+B where A and B are two polynomials.

Iutput Specification:

Output Specification:
For each test case you should output the sum of A and B in one line, with the same format as the input. Notice that there must be NO extra space at the end of each line. Please be accurate to 1 decimal place.

Sample Input:

2 1 2.4 0 3.2
2 2 1.5 1 0.5
(结尾无空行)

Sample Output:

3 2 1.5 1 2.9 0 3.2
(结尾无空行)

解答

说明：

1. eval()函数是计算值
2. 字典的get()函数，第二个参数是未查到时获得的默认值
3. 打算删除字典里的项的话，枚举keys时必须用list(d.keys())
4. sorted()排序字典得到的是tuple的list

a = [eval(i) for i in (input().split()[1:])] # 去掉第一个字符
b = [eval(i) for i in (input().split()[1:])]
d = {
    
    }
for i in range(0, len(a), 2):
    d[a[i]] = d.get(a[i], 0) + a[i+1]
for i in range(0, len(b), 2):
    d[b[i]] = d.get(b[i], 0) + b[i+1]
# 去掉coefficient为0的
for i in list(d.keys()):
    if d[i] == 0:
        del d[i]
ans = sorted(d.items(), key=lambda i:i[0], reverse=True)
res = str(len(ans))
for k,v in ans:
    res += " " + str(k) + " " + "{:.1f}".format(v)
print(res)