Problem
Implement atoi: parse a string into a 32-bit signed integer. Skip whitespace, handle optional sign, read digits, clamp to [-2³¹, 2³¹-1].
Example
Input: " -42"
Output: -42Solution
Step through: skip spaces, read sign, accumulate digits while clamping to int range.
def my_atoi(s):
INT_MAX = 2**31 - 1
INT_MIN = -2**31
s = s.lstrip()
if not s: return 0
sign = 1
i = 0
if s[0] in '+-':
sign = -1 if s[0] == '-' else 1
i = 1
result = 0
while i < len(s) and s[i].isdigit():
result = result * 10 + int(s[i])
i += 1
result *= sign
return max(INT_MIN, min(INT_MAX, result))function myAtoi(s) {
const MAX = 2**31 - 1, MIN = -(2**31);
s = s.trimStart();
if (!s) return 0;
let sign = 1, i = 0;
if (s[0] === '+' || s[0] === '-') {
sign = s[0] === '-' ? -1 : 1;
i = 1;
}
let result = 0;
while (i < s.length && /d/.test(s[i])) {
result = result * 10 + Number(s[i]);
i++;
}
result *= sign;
return Math.max(MIN, Math.min(MAX, result));
}int myAtoi(string s) {
int i = 0, n = s.size(), sign = 1;
long result = 0;
while (i < n && s[i] == ' ') i++;
if (i < n && (s[i] == '+' || s[i] == '-')) {
sign = s[i] == '-' ? -1 : 1;
i++;
}
while (i < n && isdigit(s[i])) {
result = result * 10 + (s[i] - '0');
if (result * sign > INT_MAX) return INT_MAX;
if (result * sign < INT_MIN) return INT_MIN;
i++;
}
return (int)(result * sign);
}public int myAtoi(String s) {
int i = 0, n = s.length(), sign = 1;
long result = 0;
while (i < n && s.charAt(i) == ' ') i++;
if (i < n && (s.charAt(i) == '+' || s.charAt(i) == '-')) {
sign = s.charAt(i) == '-' ? -1 : 1;
i++;
}
while (i < n && Character.isDigit(s.charAt(i))) {
result = result * 10 + (s.charAt(i) - '0');
if (result * sign > Integer.MAX_VALUE) return Integer.MAX_VALUE;
if (result * sign < Integer.MIN_VALUE) return Integer.MIN_VALUE;
i++;
}
return (int)(result * sign);
}Complexity
- Time: O(n)
- Space: O(1)
Explanation
The clamping check should happen during accumulation to avoid overflow. Use long type in C++/Java for headroom.
Comments
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