100. Convert a string to an integer

Title description

Implement the function atoi. The function of the function is to convert a string to an integer

Tip: Think carefully about all possible input situations. This question does not give input restrictions, you need to consider all possible situations yourself.

Example 1

enter

"123"

return value

123

Code implementation :

import java.util.*;


public class Solution {
    /**
     * 
     * @param str string字符串 
     * @return int整型
     */
    public int atoi (String str) {
        if (str == null && str.equals("")) {
            return 0;
        }
        boolean flag = true;
        str = str.trim();
        char[] arr = str.toCharArray();
        long result = 0;
        for (char num : arr) {
            if (num == '+') {
                continue;
            } else if (num == '-') {
                flag = false;
                continue;
            } else if (result == 0 && num == '0') {
                continue;
            } else if (num < '0' || num > '9') {
                break;
            }
            result = result * 10 + (num - '0');
        }
        if (!flag) {
            result *= -1;
        }
        if (result >= Integer.MAX_VALUE) {
            return Integer.MAX_VALUE;
        } else if (result <= Integer.MIN_VALUE) {
            return Integer.MIN_VALUE;
        }
        return (int)result;
    }
}