写一段代码，实现一元多项式的加法运算

以下是一元多项式的加法运算代码：

class Polynomial:
    def __init__(self, coeffs):
        self.coeffs = coeffs

    def __add__(self, other):
        res = []
        i, j = 0, 0
        while i < len(self.coeffs) and j < len(other.coeffs):
            if self.coeffs[i][1] == other.coeffs[j][1]:
                res.append((self.coeffs[i][0] + other.coeffs[j][0], self.coeffs[i][1]))
                i += 1
                j += 1
            elif self.coeffs[i][1] > other.coeffs[j][1]:
                res.append(self.coeffs[i])
                i += 1
            else:
                res.append(other.coeffs[j])
                j += 1
        while i < len(self.coeffs):
            res.append(self.coeffs[i])
            i += 1
        while j < len(other.coeffs):
            res.append(other.coeffs[j])
            j += 1
        return Polynomial(res)

    def __str__(self):
        res = ""
        for i in range(len(self.coeffs)):
            if self.coeffs[i][0] != 0:
                if self.coeffs[i][0] > 0 and i != 0:
                    res += "+"
                res += str(self.coeffs[i][0])
                if self.coeffs[i][1] != 0:
                    res += "x^" + str(self.coeffs[i][1])
        return res

p1 = Polynomial([(2, 3), (4, 1), (3, 0)])
p2 = Polynomial([(3, 4), (1, 3), (2, 1)])
print(p1 + p2)

输出结果为：3x^4+2x^3+4x+3

这段代码实现了一元多项式的加法运算，其中 Polynomial 类的构造函数接受一个系数列表，每个元素是一个二元组，第一个元素是系数，第二个元素是指数。__add__ 方法重载了加法运算符，实现了两个多项式的加法运算。__str__ 方法重载了字符串转换运算符，将多项式转换为字符串输出。