2011年2月26日
Not like the previous solution here http://www.tkk7.com/chaocai/archive/2012/08/05/384844.html
The following solution not using the back tracing way is more concise and readable, but for the searching space becomes huger, the performance is much worser then the previous one.
(ns SICP.unit3)(defn conflictInCol? [s col]
(some #(= col %) s)
)
(defn conflictInDia? [s col]
(let [dia (count s)
n1 (fn [c] (Math/abs (- dia (.indexOf s c))))
n2 (fn [c] (Math/abs (- col c)))]
(some #(= (n1 %) (n2 %)) s)
)
)
(defn safe? [s col]
(not (or (conflictInCol? s col) (conflictInDia? s col)))
)
(defn next-level-queens [solutions-for-prev-level board-size current-level]
(let [solutions (atom [])]
(doseq [s solutions-for-prev-level]
(doseq [col (range 0 board-size)]
(if (safe? s col)
(reset! solutions (cons (conj s col) @solutions))
)
)
)
(if (< current-level (dec board-size))
(recur @solutions board-size (inc current-level))
(count @solutions)
)
)
)
(defn queens [board-size]
(next-level-queens (apply vector (map #(vector %) (range 0 board-size))) board-size 1)
)
Chao Cai (蔡超）
Sr. SDE
Amazon
The functions to support using XPath in Clojure.
Source Code
1 ;The code was implemented by caichao@amazon.com
2 ;You could use the code anyway, but should keep the comments
3 ;Created 2012.10
4 (ns clojure.ccsoft.xml
5 (:require [clojure.xml :as xml]))
6
7 (import '(java.io StringReader)
8 '(java.io ByteArrayInputStream))
9
10 (defn xml-structure [xml-txt]
11 [ (xml/parse (-> xml-txt
12 (.getBytes)
13 (ByteArrayInputStream.)
14 )
15 )]
16 )
17
18 (defn node [tag xmlStruct]
19
20 (first (filter #(= (:tag %) tag) (:content xmlStruct)))
21 )
22
23 (defn node [path xml-txt]
24 (loop [path path
25 xml-content (xml-structure xml-txt)
26 ]
27 (let [current-tag (first path) current-elem (first xml-content)]
28 (if (= (:tag current-elem ) current-tag)
29
30 (if (= (count path) 1)
31 current-elem
32 (recur (rest path) (:content current-elem ))
33 )
34 (if (> (count xml-content) 1)
35 (recur path (rest xml-content))
36 )
37 )
38 )
39 )
40 )
How to Use
(def cmd-example "<command>
<header>
<type>script</type>
<transaction_id>12345</transaction_id>
</header>
<body>
println 3+4;
</body>
</command>")
(node [:command :header :transaction_id] cmd-example)
The following program is about solving N-Queens problem (http://en.wikipedia.org/wiki/Eight_queens_puzzle) by Clojure. If you have the better solution in Clojure or Haskell, welcome to provide your solution.
(ns queens)
(defn conflictInRow? [queens newqueen]
(some #(= newqueen %) queens)
)
(defn conflictInDia? [queens newqueen]
(let [dia (count queens)
n1 (fn [queen] (Math/abs (- dia (.indexOf queens queen))))
n2 (fn [queen] (Math/abs (- newqueen queen)))]
(some #(= (n1 %) (n2 %)) queens)
)
)
(defn conflict? [queens newqueen]
(or (conflictInRow? queens newqueen) (conflictInDia? queens newqueen))
)
(def cnt (atom 0))
(defn put-queens [queens newqueen boardSize ]
(if (= (count queens) boardSize)
(do
(println queens)
(reset! cnt (inc @cnt))
)
(do
;(println queens)
(if (> newqueen boardSize)
(if (and (= (peek queens) boardSize) (= (count queens) 1))
(throw (Exception. (str "That's all " @cnt)))
(recur (pop queens) (inc (peek queens)) boardSize )
)
(if (conflict? queens newqueen)
(recur queens (inc newqueen) boardSize )
(do
(put-queens (conj queens newqueen) 1 boardSize )
(recur queens (inc newqueen) boardSize )
)
)
)
)
)
)
(defn queens [boardSize]
(put-queens [] 1 boardSize)
)
Chao Cai (蔡超）
Sr. Software Dev Engineer
Amazon.com
1 The annotation:
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Inherited
public @interface NeedToRetry {
Class<?>[] recoverableExceptions();
int retryTime();
int intervalIncrementalFactor() default 0;
long retryInterval() default 0L;
}
2 The Aspect
@Aspect
public class InvokingRetryInterceptor {
private static Logger log = Logger.getLogger(InvokingRetryInterceptor.class);
private boolean isNeedToRetry(Throwable t,Class<?>[] recoverableExceptions){
String exceptionName= t.getClass().getName();
for (Class<?> exp:recoverableExceptions){
if (exp.isInstance(t)){
return true;
}
}
log.warn("The exception doesn't need recover!"+exceptionName);
return false;
}
private long getRetryInterval(int tryTimes,long interval,int incrementalFactor){
return interval+(tryTimes*incrementalFactor);
}
@Around(value="@annotation(amazon.internal.dropship.common.NeedToRetry)&&@annotation(retryParam)",argNames="retryParam")
public Object process(ProceedingJoinPoint pjp,NeedToRetry retryParam ) throws Throwable{
boolean isNeedTry=true;
int count=0;
Throwable fault;
Class<?>[] recoverableExceptions=retryParam.recoverableExceptions();
int retryTime=retryParam.retryTime();
long retryInterval=retryParam.retryInterval();
int incrementalFactor=retryParam.intervalIncrementalFactor();
do{
try{
return pjp.proceed();
}catch(Throwable t){
fault=t;
if (!isNeedToRetry(t,recoverableExceptions)){
break;
}
Thread.sleep(getRetryInterval(retryTime,retryInterval,incrementalFactor));
}
count++;
}while(count<(retryTime+1));
throw fault;
}
}
http://www.rkb.gov.cn/jsj/cms/s_contents/download/s_dt201103170102.html
ATDD (Acceptance Test Driven Development) is the extension of TDD, which helps us deliver exactly what the customer wants. Now ATDD has already been the hot spot in the software development world. There are several variations of ATDD including BDD, EDD and etc, also more and more frameworks have been created to help us develop with ATDD, for example FIT and JBehave.
The followings will introduce how to use the JBehave in your real project effectively.
Figure 1 Test Code Structure
Each test implementation could be divided into four layers, this structure could help us improve the codes reusability and maintainability, So, it will make us implement the tests quickly and easily.
Specification/Scenario layer:
This layer describes system’s behaviors and functionalities by the scenarios. For using JBehave, we can use the natural language describe the scenarios and just need to follow the JBehave ‘Given-When-Then’ rule.
Parser layer:
We don’t need to implement this layer , this layer has been implemented by JBehave. What exactly JBehave do is to relate the steps of the scenario to the methods of the test codes.
Step Logic Layer:
The layer implements test logics associating with every step of the scenarios. Every step are implemented by a Java method.
Action/Utils layer
This the very important layer to improve the reusability of our codes. This layer provides the utility methods to help you implement step logics. These utility methods usually involved the system state checking, mock requests sending and so on.
For example, we can provide the methods to check the data in database/file or check the state of the middleware, also so frameworks are very useful to implement the logic simulating the client browser’s requests.
Chao Cai
Working for Amazon.com
chaocai2001@yahoo.com.cn