02. Implement Atoi

The problem can be found at the following link: Question Link

My Approach

I have implemented the Atoi function using a simple iteration through the input string. Here's a breakdown of the steps:

1. Initialize a variable n to store the converted integer.

2. Iterate through the characters of the string.

   • If it's the first character and it's a '-', skip it since it represents a negative number.

   • If the character is a digit, update n by multiplying it by 10 and adding the digit.

   • If the character is not a digit, return -1 as the input is invalid.

3. Return the final integer, considering the sign.

Time and Auxiliary Space Complexity

• Time Complexity: O(N), where N is the length of the input string. We iterate through the string once.

• Auxiliary Space Complexity: O(1), as we use a constant amount of space for variables.

Code (C++)

class Solution {
public:
    int atoi(string s) {
        int n = 0; 
        for (int i = 0; i < s.length(); i++) {
            if (i == 0 && s[i] == '-') 
                continue;
            if (s[i] >= '0' && s[i] <= '9')
                n = n * 10 + s[i] - '0';
            else 
                return -1; 
        }
        return (s[0] == '-') ? -n : n;
    }
};

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