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# String to Integer (atoi)

<https://leetcode.com/problems/string-to-integer-atoi/description/>

> Implementatoito convert a string to an integer.
>
> **Hint:**&#x43;arefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.
>
> **Notes:**&#x49;t is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

## Thoughts

注意 1. 开头空白 2. 符号 3. 非数字的 4. 溢出.

## Code

```
class Solution {
    public int myAtoi(String str) {
        int res = 0, sign = 1;
        // Empty String
        if (str == null || str.length() == 0) {
            return res;
        }

        int i = 0;

        // RM white spaces
        while (str.charAt(i) == ' ') {
            i++;
        }

        // Handle signs
        if (str.charAt(i) == '+' || str.charAt(i) == '-') {
            sign = str.charAt(i) == '+' ? 1 : -1;
            i++;
        }

        // Convert number and avoid overflow
        for (; i < str.length(); i++) {
            int digit = str.charAt(i) - '0';
            if (digit >= 0 && digit <= 9) {
                if (Integer.MAX_VALUE / 10 < res || Integer.MAX_VALUE / 10 == res && Integer.MAX_VALUE % 10 < digit) {
                    return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
                }
                res = res * 10 + digit;
                //System.out.println(res + ", " + (res - digit) / 10);
            } else {
                break;
            }
        }

        return res * sign;
    }
}
```

## Analysis

时间复杂度O(N), N为str长度.