题解 | #把字符串转换成整数#

public class Solution {
    public int StrToInt(String str) {
        int ret = 0;
        int flag = 1;
        String num = "0123456789";
        if(str.isEmpty()) {
            return 0;
        }
        char ch = str.charAt(0);
        if (ch == '+') {
            flag = 1;
        }else if(ch == '-') {
            flag *= -1;
        }else {
            if(num.contains(ch+"")) {
                ret = str.charAt(0)-'0';
            }
        }
        for(int i = 1; i < str.length(); i++) {
            ch = str.charAt(i);
            if(!num.contains(ch+"")) {
                return 0;
            }
            ret = ret*10 + ch-'0';
        }
        return flag*ret;
    }
}