LeetCode_8_myAtio_String to Integer

    public static int myAtoi(String str) {        if (str.length() == 0)            return 0;        //记录值        int num = 0;        //标记是正是负        int flag = 0;        /*         * 判断是否含有空格         */        if (str.charAt(0) == ' ') {            for (int i = 1; i < str.length(); i++) {                if (str.charAt(i) != ' ') {                    str = str.substring(i);                    break;                }            }        }        /*         * 累加为整数         */        for (int i = 0; i < str.length(); i++) {            if(i == 0 &&str.charAt(i) == '-'){                flag = 1;                num = 0;                continue;            }            if( i == 0 &&str.charAt(i) == '+'){                num = 0;                continue;            }            if (str.charAt(i) - '0' > 9 ||str.charAt(i) - '0' < 0) {                break;            }            int p = str.charAt(i) - '0';            if(flag == 1)                p = -p;            /*             * 注意点三 判断是否超出int范围 ,可以用long来做              * 注意long 初始化是long l = 0l,而不是0             * ssssl = (long)num * 10 +(long)p ;这句话伤我千百遍             */            long  ssssl = 0l;            ssssl = (long)num * 10 +(long)p ;            if(ssssl > 2147483647){                num = 2147483647 ;                return num;            }else if(ssssl <  -2147483648){                num = -2147483648;                 return num;            }            else                num = num  * 10 + p;        }        return num;     }