take a string representing an integer and return the corresponding integer, and vice versa, should handle negative integers.
Implement an integer to string conversion function, and a string to integer.
Cannot use library like ‘int’.
string.digits = ‘0~9’, then index, to change str to int
better, res * (-1 if ... else 1)
- str to int
- code same, just shorter
def string_to_int(s: str) -> int:
return (-1 if s[0] == '-' else 1) * functools.reduce(
lambda running_sum, c: running_sum * 10 + string.digits.index(c),
s[s[0] in '-+':], 0)
- code
def string_to_int(s: str) -> int:
f = lambda x, y: x*10 + string.digits.index(y)
res = functools.reduce(f,s[s[0] in '-+':], 0) # need to use 0 as initial, since x*10 in the first round
# res = functools.reduce(f, s[1:], 0) # need to use 0 as initial, since x*10 in the first round
if s[0] == '-':
return -res
return res
int to string
the least significant digit in the decimal representation of r is r mod 10 423 % 10 = 3 then 423 // 10 = 42
chr(ord('0') + 3)to get str ‘3’c
def int_to_string(x):
print(x)
is_negative = False
if x < 0:
x, is_negative = -x, True
s = []
while True:
s.append(chr(ord('0') + x % 10))
x //= 10
if x == 0:
break
# Adds the negative sign back if is_negative
print(('-' if is_negative else '') + ''.join(reversed(s)))
return ('-' if is_negative else '') + ''.join(reversed(s))