正则表达式判断是否素数、解线性方程
参考文章：
http://coolshell.cn/articles/2704.html
http://www.programcreek.com/2013/10/top-10-questions-for-java-regular-expression/

java里用正则表达式判断是否素数：

public static boolean prime(int n) {  return !new String(new char[n]).matches(".?|(..+?)\\1+");}

public static void sovleLinearEquation(int result, int...params) {        if (result <= 0) {            throw new IllegalArgumentException("result must be positive");        }        if (params == null || params.length == 0) {            throw new IllegalArgumentException("params must not be empty");        }                //^(.*)\1{A?1}(.*)\2{B?1}$        StringBuilder p = new StringBuilder("^");        for (int i = 0, len = params.length; i < len; i++) {            int param = params[i];            if (param <= 0) {                throw new IllegalArgumentException("param must be positive:" + param);            }            p.append("(.*)\\").append(i + 1).append("{").append(param - 1).append("}");        }        p.append("$");        Pattern pattern = Pattern.compile(p.toString());        Matcher matcher = pattern.matcher(new String(new char[result]));        if (matcher.find()) {            StringBuilder exp = new StringBuilder();            for (int i = 0, len = params.length; i < len; i++) {                exp.append(" + ").append(params[i]).append(" * ").append(matcher.group(i + 1).length());            }            if (exp.length() > 0) {                exp.append(" = " + result);                System.out.println(exp.substring(3));            }        } else {            System.out.println("unsovleable");        }    }

sovleLinearEquation(51, 17, 12);sovleLinearEquation(115, 11, 2, 5);==》17 * 3 + 12 * 0 = 5111 * 10 + 2 * 0 + 5 * 1 = 115