class Solution:
def solve(self , s: str, t: str) -> str:
# write code here
n, m = len(s), len(t)
if n < m: # 确保 n >= m
s, t = t, s
n, m = m, n
t = '0' * (n - m) + t # 补0
ret = ''
ex = 0 # 进位标志
for i in range(n - 1, -1, -1):
r = int(s[i]) + int(t[i]) + ex
ret = str(r % 10) + ret
ex = r // 10
if ex:
ret = '1' + ret
return ret