[Python手撕]字符串相加（有正负）

num1 = input()
num2 = input()

def compare(num1,num2):
    for i in range(len(num1)):
        if num1[i]>num2[i]:
            return 0
        elif num1[i]<num2[i]:
            return 1
    return 2

# 解析符号
flag1 = 0
flag2 = 0

if num1[0] == "-":
    flag1 = 1
    num1 = num1[1:]
if num2[0] == "-":
    flag2 = 1
    num2 = num2[1:]

# 对齐数位
num1_len = len(num1)
num2_len = len(num2)

if num1_len < num2_len:
    for _ in range(num2_len - num1_len):
        num1 ="0" + num1
else:
    for _ in range(num1_len - num2_len):
        num2 ="0" + num2

# 制作返回数组

num1_arr = [int(c) for c in num1]
num2_arr = [int(c) for c in num2]
length = len(num1)

if flag1 == 0 and flag2 == 0:
    res = [0]*(length+1)
    temp = 0
    for i in range(length-1,-1,-1):
        if num1_arr[i]+num2_arr[i]+temp >= 10:
            res[i+1] = num1_arr[i]+num2_arr[i]+temp -10
            temp = 1
        else:
            res[i+1] = num1_arr[i]+num2_arr[i]+temp
            temp = 0
    if temp == 1:
        res[0] = 1

    if res[0] == 1:
        print("".join(str(c) for c in res))
    else:
        print("".join(str(c) for c in res[1:]))
if flag1 == 1 and flag2 == 1:
    res = [0]*(length+1)
    temp = 0
    for i in range(length-1,-1,-1):
        if num1_arr[i]+num2_arr[i]+temp >= 10:
            res[i+1] = num1_arr[i]+num2_arr[i]+temp -10
            temp = 1
        else:
            res[i+1] = num1_arr[i]+num2_arr[i]+temp
            temp = 0
    if temp == 1:
        res[0] = 1

    if res[0] == 1:
        print("-"+"".join(str(c) for c in res))
    else:
        print("-"+"".join(str(c) for c in res[1:]))
if flag1 == 1 and flag2 == 0:
    res = [0]*length
    if compare(num1_arr,num2_arr) == 0:
        for i in range(length-1,-1,-1):
            if num1_arr[i]>=num2_arr[i]:
                res[i] = num1_arr[i] - num2_arr[i]
            else:
                num1_arr[i-1] -= 1
                res[i] = num1_arr[i]+10 - num2_arr[i]
        for i in range(len(res)):
            if res[i] != 0:
                print("-"+"".join(str(c) for c in res[i:]))
                break
    elif compare(num1_arr,num2_arr) == 1:
        for i in range(length-1,-1,-1):
            if num2_arr[i]>=num1_arr[i]:
                res[i] = num2_arr[i] - num1_arr[i]
            else:
                num2_arr[i-1] -= 1
                res[i] = num2_arr[i]+10 - num1_arr[i]
        for i in range(len(res)):
            if res[i] != 0:
                print("".join(str(c) for c in res[i:]))
                break
    elif compare(num1_arr,num2_arr) == 2:
        print("0")
if flag1 == 0 and flag2 == 1:
    res = [0]*length
    if compare(num1_arr,num2_arr) == 0:
        for i in range(length-1,-1,-1):
            if num1_arr[i]>=num2_arr[i]:
                res[i] = num1_arr[i] - num2_arr[i]
            else:
                num1_arr[i-1] -= 1
                res[i] = num1_arr[i]+10 - num2_arr[i]
        for i in range(len(res)):
            if res[i] != 0:
                print("".join(str(c) for c in res[i:]))
                break
    elif compare(num1_arr,num2_arr) == 1:
        for i in range(length-1,-1,-1):
            if num2_arr[i]>=num1_arr[i]:
                res[i] = num2_arr[i] - num1_arr[i]
            else:
                num2_arr[i-1] -= 1
                res[i] = num2_arr[i]+10 - num1_arr[i]
        for i in range(len(res)):
            if res[i] != 0:
                print("-"+"".join(str(c) for c in res[i:]))
                break
    elif compare(num1_arr,num2_arr) == 2:
        print("0")