算法之求String类型算数表达式的值 和 验证IP地址合法性

import org.apache.commons.validator.routines.InetAddressValidator;

public class IPValidator
{
    public static Boolean checkIpValid(String str)
    {
        // Get an InetAddressValidator
        InetAddressValidator validator = InetAddressValidator.getInstance();
        if (validator.isValidInet4Address(str) || validator.isValidInet6Address(str)) return true;
        return false;
    }

    public static void main(String[] args)
    {
        // an IPv4 address
          final String ipv4 = "10.8.9.28";

        // an IPv6 address
          final String ipv6 =
                "2001:0db8:85a3:0000:0000:8a2e:0370:7334";
        // Get an InetAddressValidator
        Boolean res4 = checkIpValid(ipv4);
        System.out.println("res4 = " + res4);
        Boolean res6 = checkIpValid(ipv6);
        System.out.println("res6 = " + res6);

    }
}

import java.util.Stack;

class Calculator {

    final static Stack<Character> opStack = new Stack<>();

    /**
     * calculate the value of the suffix expression
     * @param expr - the input string expression
     * @return - result of the expression
     */
    public static int calc(String expr){
        // transfer the string format from infix to suffix
        String suffix = transferToSuffix(expr);
        Stack<Integer> resStack = new Stack<>();
        char[] arr = suffix.toCharArray();
        for(char ch : arr)
        {
            if (Character.isDigit(ch)) resStack.push(Integer.valueOf(ch - '0'));
            else resStack.push(calResWithOperation(ch, resStack.pop(), resStack.pop()));
        }
        return resStack.pop();
    }

    /**
     * transfer the string format from infix to suffix
     * @param expr - String in the form of infix
     * @return String in the form of suffix
     */
    private static String transferToSuffix(String expr){
        char[] arr = expr.replaceAll(" ","").toCharArray();
        int len = arr.length;
        String suffix = "";

        for(int i = 0; i < len; i++)
        {
            char ch = arr[i];
            // output if the char is number
            if(Character.isDigit(ch))
            {
                suffix+=ch;
                continue;
            }

            // push to the stack directly if char is '('
            if(ch == '(') {
                opStack.push(ch);
                continue;
            }

            if(ch == '+' || ch == '-'){
                while(!opStack.empty() && (opStack.peek() != '('))
                    suffix+= opStack.pop();
                opStack.push(ch);
                continue;
            }

            if(ch == '*' || ch == '/'){
                while(!opStack.empty() && (opStack.peek() == '*' || opStack.peek() == '/'))
                    suffix+= opStack.pop();
                opStack.push(ch);
                continue;
            }

            // pop the stack
            if(ch == ')'){
                while(!opStack.empty() && opStack.peek() != '(')
                    suffix += opStack.pop();
                opStack.pop();
                continue;
            }
        }

        while(!opStack.empty()) suffix += opStack.pop();
        return suffix;
    }

    /**
     * calculate the two numbers with operation
     *
     * @param op the operation symbol
     * @param num1 the calculated number
     * @param num2 the calculated number
     * @return the calculate result
     */
    private static int calResWithOperation(char op, int num1, int num2){
        if (op == '+') return num2 + num1;
        else if (op == '-') return num2 - num1;
        else if (op == '*') return num2 * num1;
        else if (op == '/') return num2 / num1;
        else return 0;
    }

      public static void main(String[] args){
        String exp = "1+2* (3+4)";
        String postfix = transferToSuffix(exp);
        System.out.println("postfix = " + postfix); // postfix = 1234+*+
        int res = calc(postfix);
        System.out.println("res = " + res);  // res = 15
    }
}