## Algorithm

Problem Name: 8. String to Integer (atoi)

Implement the `myAtoi(string s)` function, which converts a string to a 32-bit signed integer (similar to C/C++'s `atoi` function).

The algorithm for `myAtoi(string s)` is as follows:

2. Check if the next character (if not already at the end of the string) is `'-'` or `'+'`. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present.
3. Read in next the characters until the next non-digit character or the end of the input is reached. The rest of the string is ignored.
4. Convert these digits into an integer (i.e. `"123" -> 123`, `"0032" -> 32`). If no digits were read, then the integer is `0`. Change the sign as necessary (from step 2).
5. If the integer is out of the 32-bit signed integer range `[-231, 231 - 1]`, then clamp the integer so that it remains in the range. Specifically, integers less than `-231` should be clamped to `-231`, and integers greater than `231 - 1` should be clamped to `231 - 1`.
6. Return the integer as the final result.

Note:

• Only the space character `' '` is considered a whitespace character.
• Do not ignore any characters other than the leading whitespace or the rest of the string after the digits.

Example 1:

```Input: s = "42"
Output: 42
Explanation: The underlined characters are what is read in, the caret is the current reader position.
Step 1: "42" (no characters read because there is no leading whitespace)
^
Step 2: "42" (no characters read because there is neither a '-' nor '+')
^
Step 3: "42" ("42" is read in)
^
The parsed integer is 42.
Since 42 is in the range [-231, 231 - 1], the final result is 42.
```

Example 2:

```Input: s = "   -42"
Output: -42
Explanation:
^
Step 2: "   -42" ('-' is read, so the result should be negative)
^
Step 3: "   -42" ("42" is read in)
^
The parsed integer is -42.
Since -42 is in the range [-231, 231 - 1], the final result is -42.
```

Example 3:

```Input: s = "4193 with words"
Output: 4193
Explanation:
Step 1: "4193 with words" (no characters read because there is no leading whitespace)
^
Step 2: "4193 with words" (no characters read because there is neither a '-' nor '+')
^
Step 3: "4193 with words" ("4193" is read in; reading stops because the next character is a non-digit)
^
The parsed integer is 4193.
Since 4193 is in the range [-231, 231 - 1], the final result is 4193.
```

Constraints:

• `0 <= s.length <= 200`
• `s` consists of English letters (lower-case and upper-case), digits (`0-9`), `' '`, `'+'`, `'-'`, and `'.'`.

## Code Examples

### #1 Code Example with C Programming

```Code - C Programming```

``````
int myAtoi(char* str) {
int d, k = 0, negative = 0;

if (!str) return 0;

while (*str == ' ') str ++;

if (*str == '+') {
str ++;

negative = 1;
str ++;
}

while (*str >= '0' && *str <= '9') {
d = *str - '0';
str ++;
if (negative == 0) {
if (k > (0x7fffffff - d) / 10) {        // possitive number overflow
return 0x7fffffff;
}
k = k * 10 + d;
} else {
if (k < ((signed)0x80000000 + d) / 10) {    // negative number overflow
return 0x80000000;
}
k = k * 10 - d;
}
}
return k;
}

``````
Copy The Code &

Input

cmd
s = "42"

Output

cmd
42

### #2 Code Example with C++ Programming

```Code - C++ Programming```

``````
class Solution {
public:
int myAtoi(string str) {
if (str.size() == 0) return 0;
int cur = 0;
while (cur < str.size() && str[cur] == ' ') cur++;
if (cur == str.size() || (!isdigit(str[cur]) && str[cur] != '+' && str[cur] != '-')) return 0;
int end = cur + 1;
while (isdigit(str[end])) end++;
string s = str.substr(cur, end - cur);
int num = 0;
int base = 1;
for (int i = s.size() - 1; i >= 0; i--) {
if (s[i] == '+' || s[i] == '-') break;
int add = base * (s[i] - '0');
if (INT_MAX - num < add || (s.size() - i > 10 && s[i] != '0'))
return s == '-' ? INT_MIN : INT_MAX;
base *= 10;
}
if (s == '-') num = -num;
return num;
}
};
``````
Copy The Code &

Input

cmd
s = " -42"

Output

cmd
-42

### #3 Code Example with Java Programming

```Code - Java Programming```

``````
class Solution {
public int myAtoi(String s) {
int idx = 0;
int n = s.length();
while (idx < n && s.charAt(idx) == ' ') {
idx++;
}
int sign = 1;
if (idx < n && (s.charAt(idx) == '-' || s.charAt(idx) == '+')) {
sign = s.charAt(idx) == '-' ? -1 : 1;
idx++;
}
if (idx == n || !Character.isDigit(s.charAt(idx))) {
return 0;
}
while (idx < n && s.charAt(idx) == '0') {
idx++;
}
int number = 0;
while (idx < n && Character.isDigit(s.charAt(idx))) {
int digit = Character.getNumericValue(s.charAt(idx));
if ((number > Integer.MAX_VALUE / 10) || (number == Integer.MAX_VALUE / 10 && digit > Integer.MAX_VALUE % 10)) {
return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
}
number = number * 10 + digit;
idx++;
}
return number * sign;
}
}
``````
Copy The Code &

Input

cmd
s = "4193 with words"

Output

cmd
4193

### #4 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
const myAtoi = function(str) {
return Math.max(Math.min(parseInt(str) || 0, 2147483647), -2147483648);
};
``````
Copy The Code &

Input

cmd
s = "42"

Output

cmd
42

### #5 #4 Code Example with Another Javascript Programming

```Code - Javascript Programming```

``````
const myAtoi = function(s) {
let n = s.length, i = 0, j = 0, sign = 1;
if(n === 0) {
return 0;
}
while(i < n && s[i] === ' ') {
i++;
}
if(i < n && (s[i] === '-' || s[i] === '+')) {
sign = (s[i] === '-') ? -1 : 1;
i++;
}
j = i
while(i < n) {
if(Number.isInteger(parseInt(s[i]))) i++;
else break;
}
let result = parseInt(s.slice(j, i))
if(isNaN(result)) return 0
if(sign * result < -(2**31)) return -(2**31);
else if(sign * result > (2**31-1)) return 2**31-1;
else return sign * result;
};
``````
Copy The Code &

Input

cmd
s = " -42"

Output

cmd
-42

### #6 Code Example with Python Programming

```Code - Python Programming```

``````
class Solution:
def myAtoi(self, str):
r = [int(c) for c in re.findall(r"^[-+]?\u005Cd+", str.lstrip())]
return (r and 2 ** 31 - 1 < r and 2 ** 31 - 1) or (r and r < -2 ** 31 and -2 ** 31) or (r and r) or 0
``````
Copy The Code &

Input

cmd
s = "42"

Output

cmd
42