8. String to Integer (atoi)

Problem Description

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:

1. Read in and ignore any leading whitespace.
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. If neither is present, assume the result is positive.
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.

Examples

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 1: "   -42" (leading whitespace is read and ignored)
            ^
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.

class Solution:
    def myAtoi(self, s: str) -> int:
        s = s.strip()
        if not s:
            return 0
            
        sign = 1
        result = 0
        i = 0
        
        if s[0] in ['+', '-']:
            sign = 1 if s[0] == '+' else -1
            i += 1
            
        while i < len(s) and s[i].isdigit():
            digit = int(s[i])
            if result > (2**31 - 1) // 10 or (result == (2**31 - 1) // 10 and digit > 7):
                return 2**31 - 1 if sign == 1 else -2**31
            if result < -2**31 // 10 or (result == -2**31 // 10 and digit > 8):
                return -2**31
            result = result * 10 + sign * digit
            i += 1
            
        return result

class Solution {
    public int myAtoi(String s) {
        s = s.trim();
        if (s.isEmpty()) {
            return 0;
        }
        
        int sign = 1;
        int result = 0;
        int i = 0;
        
        if (s.charAt(0) == '+' || s.charAt(0) == '-') {
            sign = s.charAt(0) == '+' ? 1 : -1;
            i++;
        }
        
        while (i < s.length() && Character.isDigit(s.charAt(i))) {
            int digit = s.charAt(i) - '0';
            if (result > Integer.MAX_VALUE / 10 || 
                (result == Integer.MAX_VALUE / 10 && digit > Integer.MAX_VALUE % 10)) {
                return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
            }
            if (result < Integer.MIN_VALUE / 10 || 
                (result == Integer.MIN_VALUE / 10 && digit > -(Integer.MIN_VALUE % 10))) {
                return Integer.MIN_VALUE;
            }
            result = result * 10 + sign * digit;
            i++;
        }
        
        return result;
    }
}

class Solution {
public:
    int myAtoi(string s) {
        // Remove leading whitespace
        s.erase(0, s.find_first_not_of(" "));
        if (s.empty()) {
            return 0;
        }
        
        int sign = 1;
        int result = 0;
        int i = 0;
        
        if (s[0] == '+' || s[0] == '-') {
            sign = s[0] == '+' ? 1 : -1;
            i++;
        }
        
        while (i < s.length() && isdigit(s[i])) {
            int digit = s[i] - '0';
            if (result > INT_MAX / 10 || 
                (result == INT_MAX / 10 && digit > INT_MAX % 10)) {
                return sign == 1 ? INT_MAX : INT_MIN;
            }
            if (result < INT_MIN / 10 || 
                (result == INT_MIN / 10 && digit > -(INT_MIN % 10))) {
                return INT_MIN;
            }
            result = result * 10 + sign * digit;
            i++;
        }
        
        return result;
    }
};

/**
 * @param {string} s
 * @return {number}
 */
var myAtoi = function(s) {
    s = s.trim();
    if (!s) {
        return 0;
    }
    
    let sign = 1;
    let result = 0;
    let i = 0;
    
    if (s[0] === '+' || s[0] === '-') {
        sign = s[0] === '+' ? 1 : -1;
        i++;
    }
    
    while (i < s.length && /\d/.test(s[i])) {
        const digit = parseInt(s[i]);
        if (result > Math.floor(Number.MAX_SAFE_INTEGER / 10) || 
            (result === Math.floor(Number.MAX_SAFE_INTEGER / 10) && 
             digit > Number.MAX_SAFE_INTEGER % 10)) {
            return sign === 1 ? Number.MAX_SAFE_INTEGER : Number.MIN_SAFE_INTEGER;
        }
        if (result < Math.floor(Number.MIN_SAFE_INTEGER / 10) || 
            (result === Math.floor(Number.MIN_SAFE_INTEGER / 10) && 
             digit > -(Number.MIN_SAFE_INTEGER % 10))) {
            return Number.MIN_SAFE_INTEGER;
        }
        result = result * 10 + sign * digit;
        i++;
    }
    
    return result;
};

public class Solution {
    public int MyAtoi(string s) {
        s = s.Trim();
        if (string.IsNullOrEmpty(s)) {
            return 0;
        }
        
        int sign = 1;
        int result = 0;
        int i = 0;
        
        if (s[0] == '+' || s[0] == '-') {
            sign = s[0] == '+' ? 1 : -1;
            i++;
        }
        
        while (i < s.Length && char.IsDigit(s[i])) {
            int digit = s[i] - '0';
            if (result > int.MaxValue / 10 || 
                (result == int.MaxValue / 10 && digit > int.MaxValue % 10)) {
                return sign == 1 ? int.MaxValue : int.MinValue;
            }
            if (result < int.MinValue / 10 || 
                (result == int.MinValue / 10 && digit > -(int.MinValue % 10))) {
                return int.MinValue;
            }
            result = result * 10 + sign * digit;
            i++;
        }
        
        return result;
    }
}