## String to Integer (atoi)

06/23/2016 Math String

## Question

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

## Solution

Result: Accepted Time: 4ms

Here should be some explanations.

int myAtoi(char* str) {
const long long limit = 0x7fffffff;
long long ans = 0;
if(str == NULL)
return 0;
int idx = 0;
while(str[idx] != '\n')
if(str[idx] ==' ' || str[idx] == '\n' || str[idx] == '\t')
idx++;
else
break;
int st = idx;
if(str[idx] =='+' || str[idx] == '-')
st = idx + 1;
for(; isdigit(str[st]) && st < 12+idx; st++)
{
ans = ans*10 + (long long)(str[st] - '0');
}
if(str[idx] != '-' && ans > limit)
return 0x7fffffff;
if(str[idx] == '-' && ans > limit + 1)
return 0x80000000;
if(str[idx] == '-')
return (int) -ans;
return (int)(ans);
}


Complexity Analytics

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$