8. String to Integer (atoi).cpp

[ayushHardeniya]

8. String to Integer (atoi).cpp

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Intuition

This problem is basically about turning a string into an integer, like the C function atoi().
My thought process was simple: skip spaces, check the sign, read the digits, and stop at the first non-digit.
Also, we need to make sure the number stays within the int range to avoid overflow or underflow.

---

Approach

1. Skip spaces at the start so we only deal with the real number.
2. Check for '+' or '-' to know if the result should be positive or negative.
3. Read digits one by one and build the number (ans = ans * 10 + digit).
4. Handle overflow/underflow: before adding a new digit, check if it goes beyond INT_MAX or below INT_MIN.
5. Return the result multiplied by the sign.

• Time Complexity: O(n) - we go through the string once.
• Space Complexity: O(1) - just a few variables used.

---

Code Solution (C++)

class Solution {
public:
    int myAtoi(string s) {
        int i = 0, n = s.size(), sign = 1;
        long ans = 0;

        // Skip leading spaces
        while (i < n && s[i] == ' ') i++;

        // Check sign
        if (i < n && (s[i] == '+' || s[i] == '-')) {
            sign = (s[i] == '-') ? -1 : 1;
            i++;
        }

        // Build the number
        while (i < n && isdigit(s[i])) {
            int digit = s[i] - '0';

            // Overflow/Underflow check
            if (ans > (INT_MAX - digit) / 10)
                return sign == 1 ? INT_MAX : INT_MIN;

            ans = ans * 10 + digit;
            i++;
        }

        return ans * sign;
    }
};

## Summary by Sourcery

New Features:
- Implement myAtoi that trims leading spaces, detects optional '+' or '-' sign, parses continuous digit characters, and clamps overflow to INT_MAX/INT_MIN in O(n) time and O(1) space

[sourcery-ai]

Reviewer's Guide

Implements the myAtoi function by trimming leading spaces, determining sign, accumulating digits into a 64-bit accumulator with overflow/underflow checks, and returning a clamped int result.

Class diagram for the new Solution class implementing myAtoi

classDiagram
class Solution {
  +int myAtoi(string s)
}

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Flow diagram for the myAtoi string to integer conversion process

flowchart TD
    A["Start"] --> B["Trim leading spaces"]
    B --> C["Check if string is empty after trimming"]
    C -->|Empty| D["Return 0"]
    C -->|Not empty| E["Check sign (+/-)"]
    E --> F["Iterate over digits"]
    F --> G["Accumulate number (ans = ans * 10 + digit)"]
    G --> H["Check for overflow/underflow"]
    H -->|Overflow/Underflow| I["Return INT_MAX/INT_MIN"]
    H -->|No overflow| J["Continue iteration"]
    J --> F
    F -->|No more digits| K["Return ans * sign as int"]

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File-Level Changes

Change	Details	Files
Preprocess input and handle empty input	Skip leading spaces via while loop Check if index reached string length and return 0	8. String to Integer (atoi).cpp
Determine numeric sign	Detect '-' to set sign = -1 and increment index Detect '+' to leave sign positive and increment index	8. String to Integer (atoi).cpp
Accumulate digits and detect overflow/underflow	Loop while characters are digits and update ans = ans * 10 + digit After each update, compare against INT_MAX/INT_MIN and return clamped value	8. String to Integer (atoi).cpp
Finalize and return result	Multiply accumulated value by sign Cast result to int for return	8. String to Integer (atoi).cpp

Possibly linked issues

• 322. Coin Change #8: The PR provides the C++ solution for LeetCode problem 8, String to Integer (atoi), as described in the issue.

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[github-actions]

Thanks for raising the PR, the owner will be review it soon' keep patience, keep contributing>>>!!! make sure you have star ⭐ the repo

[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• Change the signature to int myAtoi(const string& s) to avoid copying the input string on each call.
• Instead of accumulating into a long long and checking for overflow afterward, pre-check ans > INT_MAX/10 or (ans == INT_MAX/10 && digit > INT_MAX%10) to handle overflow without needing a wider type.
• Use more descriptive variable names (e.g. n or length instead of l) to improve code readability.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Change the signature to `int myAtoi(const string& s)` to avoid copying the input string on each call.
- Instead of accumulating into a `long long` and checking for overflow afterward, pre-check `ans > INT_MAX/10` or `(ans == INT_MAX/10 && digit > INT_MAX%10)` to handle overflow without needing a wider type.
- Use more descriptive variable names (e.g. `n` or `length` instead of `l`) to improve code readability.

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[SjxSubham]

@ayushHardeniya
all looks good

Star the repo⭐ as well ...