【leetcode】8.String to Integer (atoi)

8. String to Integer (atoi)

Implement atoi to convert a string to an integer.

Hint: Carefully 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: It 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.

Tips: 本题要自己实现atoi函数，需要声明的包括：

①.java 字符串或者字符数组结尾处并不包含"".

②考虑输入的字符串前面有很多空格。

③考虑'+','_'

④我没通过的case有"    -12a42",正确输出为 -12。

　　"2147483648" 正确输出为 2147483647

package medium;

public class L8StringToInteger_atoi {

    public int myAtoi(String str) {
        if (str == "")
            return 0;
        long num = 0;
        int minus = 1;// +
        int i = 0;
        int len = str.length();
        while (i < len) {
            if (str.charAt(i) == ' ') {
                i++;
            }else{
　　　　　　　　　　break;
　　　　　　　}
        }
        if (str != null && i < len) {
            if (str.charAt(i) == '+') {
                minus = 1;
                i++;
            } else if (str.charAt(i) == '-') {
                minus = -1;
                i++;
            } 
            while (i < len) {
                System.out.println(i + " " + str.charAt(i));
                if (str.charAt(i) >= '0' && str.charAt(i) <= '9') {
                    num = num * 10 + minus * (str.charAt(i) - '0');
                    if ((minus == 1 && num >= 2147483647) ) {
                        num = 2147483647;
                        break;
                    }if( (minus == -1 && num < -2147483648)){
                        num=-2147483648;
                        break;
                    }
                    i++;
                    System.out.println(i);
                } else {
                    
                    break;
                }
            }
        }
        return (int) num;
    }

    public static void main(String[] args) {
        String str = "  -0012a42";
        L8StringToInteger_atoi l8 = new L8StringToInteger_atoi();
        int num = l8.myAtoi(str);
        System.out.println(num);
    }
}