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授课教师:Wuhan University 赵老师zj@webturing.com
public static boolean isNumber(String tok) {
try {
Double.parseDouble(tok);
return true;
} catch (Exception e) {
return false;
}
}
public static double eval(List<String> exp) {
Stack<Double> S = new Stack<>();
for (String tok : exp) {
if (isNumber(tok)) {
S.push(Double.parseDouble(tok));
} else {
if (S.isEmpty()) {
return ERROR;
}
double b = S.peek();
S.pop();
if (S.isEmpty()) {
return ERROR;
}
double a = S.peek();
S.pop();
double c = 0;
switch (tok) {
case "+":
c = a + b;
break;
case "-":
c = a - b;
break;
case "*":
c = a * b;
break;
case "/":
if (b == 0) return ERROR;
c = a / b;
break;
}
S.push(c);
}
}
return S.size() != 1 ? ERROR : S.peek();
}
public static double eval(String[] exp) {
return eval(Arrays.asList(exp));
}
public static double eval(String s) {
return eval(s.split("\\s+"));
}
java方法设计中的委托delegate*
随即求解器的基本思想:shuffle
随机运算符的产生
搜索的时间控制（找不到解的处理，最大搜索次数）
private static String randSearcher(int[] a) {
for (int j = 0; j < 4 * 4 * 4; j++) {
String[] ops = new String[3];
int x = j / 16;
int y = j % 16 / 4;
int z = j % 4;
ops[0] = OPS[x];
ops[1] = OPS[y];
ops[2] = OPS[z];
List<String> exp = new Vector<>();
for (Integer i : a) {
exp.add(Integer.toString(i));
}
for (String op : ops) {
exp.add(op);
}
int tot = 0;
while (++tot < MAX_RAND_SEARCH_COUNT) {
Collections.shuffle(exp);
double result = RPolandExpression.eval(exp);
if (result == 24) {
return (exp).toString();
}
}
}
return "No solution";
}
public static String solve24(int a, int b, int c, int d) {
return randSearcher(new int[]{a,b,c,d});
}
运算数判断
public static boolean isNumber(String s) {//巧妙利用异常机制来处理 也可以使用正则表达式来判断
try{
Double.parseDouble(s);
return true;
}catch(NumberFormatException e){
return false;
}
}
字符串String/StringBuffer/StringBuilder/char[]
输入输出 File/Scanner/….
异常处理 Exception Handling
集合框架 java.uitl. Stack
日期/高精度
随机数: //游戏开发必备技能
Math.random()
java.util.Random()
Collections.shuffle(List s)
public class RandDemo {
static Random rand = new Random();
public static void main(String[] args) {
System.out.println(Math.random());//产生0-1之间的随机小数
System.out.println(rand.nextInt(10));//产生[0,10)之间的随机整数
List<Integer> balls = new ArrayList<Integer>();
for (int i = 1; i <= 15; i++)
balls.add(i);
System.out.println(balls);
Collections.shuffle(balls);
System.out.println(balls);
List<Integer> firstPrize = balls.subList(0, 6);
System.out.println("First Prize:" + firstPrize);
}
}
递归定义
java实现链式结构非常方便
public void midVisit() {
System.out.print("(");
if(left!=null)left.midVisit();
System.out.print(root);
if(right!=null)right.midVisit();
System.out.print(")");
}
public BinaryTree(String root) { this(root,null,null);//构造方法的重载}
public BinaryTree(String root, BinaryTree left, BinaryTree right) {
this.root = root;
this.left = left;
this.right = right;
}
public String getRoot() { return root;}
public void setRoot(String root) { this.root = root;}
public BinaryTree getLeft() { return left;}
public void setLeft(BinaryTree left) { this.left = left;}
public BinaryTree getRight() { return right;}
public void setRight(BinaryTree right) { this.right = right;}
String root;
BinaryTree left;
BinaryTree right;
/**
* 根据后缀式还原二叉树
* @param 后缀表达式exp
* @return 一个二叉树tree 其后序遍历为exp
*/
public static BinaryTree createTree(String[] exp) {
Stack<BinaryTree> stack=new Stack<BinaryTree>();
for(String s:exp){
if(Evaluator.isNumber(s)){
BinaryTree t=new BinaryTree(s);
stack.push(t);
}else if (Evaluator.isOperator(s)){
BinaryTree t=new BinaryTree(s);// operator
BinaryTree right=stack.pop();
BinaryTree left=stack.pop();
t.setLeft(left);
t.setRight(right);
stack.push(t);
}
}
return stack.peek();
}
public void midVisit() {
System.out.print("(");
if(left!=null)left.midVisit();
System.out.print(root);
if(right!=null)right.midVisit();
System.out.print(")");
}
public void midVisit(StringBuffer buffer) {
if (braced)
buffer.append("(");
if (left != null)
left.midVisit(buffer);
buffer.append(root);
if (right != null)
right.midVisit(buffer);
if (braced)
buffer.append(")");
}
public void setLeft(BinaryTree left) {
this.left = left;
left.braced = Evaluator.less(left.root, root);
}
public void setRight(BinaryTree right) {
this.right = right;
right.braced = Evaluator.lessOrEqual(root, right.root);
}
public static boolean lessOrEqual(String a, String b) {
return Arrays.asList("-- -+ *+ *- */ /+ /- /* //".split(" ")).contains(
a + b);
}
public static boolean less(String a, String b) {
return Arrays.asList("+* +/ -* -/".split(" ")).contains(a + b);
}
###康拓逆展开: 0~n！-1 映射为 全排列
/**
* 逆康拓展开，根据数值直接生成排列
* @param x
* @param m
* @return
*/
static final int FAC[] = { 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880 };
public static int[] codel(int x, int m) {
int[] label = new int[m];
int[] n = new int[m];
int cnt;
for (int i = 0; i < m; i++)
label[i] = 1;
for (int i = 0; i < m; i++) {
cnt = x / FAC[m - 1 - i];
x = x % FAC[m - 1 - i];
for (int j = 0; j < m; j++) {
if (label[j] == 0)
continue;
if (cnt == 0) {
label[j] = 0;
n[i] = j;
break;
}
cnt--;
}
}
return n;
}
public static List<String> bruteSearch(int[] arr) {
List<String> exp=new ArrayList<String>();
for (int cc = 0; cc < Permutation.FAC[4]; cc++) {
int[] idx = Permutation.codel(cc, 4);
String a = String.valueOf(arr[idx[0]]);
String b = String.valueOf(arr[idx[1]]);
String c = String.valueOf(arr[idx[2]]);
String d = String.valueOf(arr[idx[3]]);
for (int i = 0; i < 4; i++)
for (int j = 0; j < 4; j++)
for (int k = 0; k < 4; k++) {
String X = Point24.OPS[i];
String Y = Point24.OPS[j];
String Z = Point24.OPS[k];
for (String[] ee : new String[][] {
{ a, b, X, c, Y, d, Z },
{ a, b, c, X, Y, d, Z },
{ a, b, X, c, d, Y, Z },
{ a, b, c, X, d, Y, Z },
{ a, b, c, d, X, Y, Z }, }) {
if (Evaluator.eval(ee) == Point24.GOAL) {
exp.addAll(Arrays.asList(ee));
return exp;
}
}
}
}
exp.clear();
return exp;
}
int[] arr = new int[]{a, b, c, d};
Arrays.sort(arr);
String key = Arrays.toString(arr);
String result = query(key);//先查询数据库
if (result == null) {
System.err.println("重新计算结果并写入数据库");
result = ai.Engine.solve24(a, b, c, d);
save(key, result);//保留计算结果
}
long end=System.currentTimeMillis();
request.getSession().setAttribute("result", result);
request.getSession().setAttribute("elapse", (end-start)/1000.0);
response.sendRedirect("index.jsp");
public class SolveServlet extends HttpServlet {
private String diverClass;
private String userName;
private String password;
private String url;
private Connection connection;
private Statement stmt;
@Override
public void init() throws ServletException {
diverClass = /* getServletConfig(). */getServletContext().getInitParameter("driver");
userName = /* getServletConfig(). */getServletContext().getInitParameter("username");
password = /* getServletConfig(). */getServletContext().getInitParameter("password");
url = /* getServletConfig(). */getServletContext().getInitParameter("url");
try {
Class.forName(diverClass);
} catch (Exception e) {
e.printStackTrace();
}
}
Web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1">
<context-param>
<param-name>driver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</context-param>
<context-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://#############:3306/ahstu</param-value>
</context-param>
<context-param>
<param-name>username</param-name>
<param-value>#####</param-value>
</context-param>
<context-param>
<param-name>password</param-name>
<param-value>######</param-value>
</context-param>
</web-app>
private String query(String key) {
String ans = null;
try {
connection = DriverManager.getConnection(url, userName, password);
stmt = connection.createStatement();//key
PreparedStatement ps = connection.prepareStatement("select solution from point24 where numbers=? LIMIT 1");
ps.setString(1, key);
ResultSet rs = ps.executeQuery();
if (rs.next()) {
ans = rs.getString(1);
System.err.println("数据已经存在，直接读取数据库");
}
rs.close();
stmt.close();
connection.close();
} catch (Exception e) {
e.printStackTrace();
System.err.println("数据库链接失败");
}
return ans;
}
private boolean save(String key, String result) {
try {
connection = DriverManager.getConnection(url, userName, password);
stmt = connection.createStatement();
PreparedStatement ps = connection.prepareStatement("insert into point24(numbers,solution) value(?,?)");
ps.setString(1, key);
ps.setString(2, result);
int x = ps.executeUpdate();
System.err.println("写入数据库成功");
stmt.close();
connection.close();
return x > 0;
} catch (Exception e) {
e.printStackTrace();
System.err.println("数据库链接失败");
return false;
}
}
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