java语言程序设计第二十章部分答案1，4，11，14，16题

1.

public class Test2001 {
public static void main(String[] args) throws FileNotFoundException {
    File file=new File("D:\1code\test.txt");
    Scanner input=new Scanner(file);
        Collection<String> collection=new ArrayList<>(); 

        while(input.hasNext()) {
            collection.add(input.next());
        }

    PriorityQueue<String> word=new PriorityQueue(collection);


        String c;
        while((c=word.poll())!=null) {
            System.out.println(c);
        }


}

}
4.

public class Test2004 {
public static void main(String[] args) {
    Point[] point =new Point[100];
    CompareY[] comparey=new CompareY[100];
    for(int i=0;i<100;i++) {
        point[i]=new Point((int)(Math.random()*100),(int)(Math.random()*100));

    }
    Arrays.sort(point);
    for(int i=0;i<100;i++)
        System.out.println(point[i].getX()+"  "+point[i].getY());
    Arrays.sort(point,new CompareY());
    for(int i=0;i<100;i++) {
        System.out.println(point[i].getX()+"  "+point[i].getY());
    }

}

}

class Point implements Comparable<Point>{
private int x;
private int y;
public Point() {
    this.x=0;
    this.y=0;
}
public Point(int x, int y) {
    super();
    this.x = x;
    this.y = y;
}
public int getX() {
    return x;
}
public void setX(int x) {
    this.x = x;
}
public int getY() {
    return y;
}
public void setY(int y) {
    this.y = y;
}
@Override
public int compareTo(Point o) {
    // TODO Auto-generated method stub
    if(this.getX()>o.getX())
        return 1;
    else if(this.getX()<o.getX())
        return -1;
    else if(this.getY()>o.getY())
        return 1;
    else if(this.getY()<o.getY())
        return -1;
    else
        return 0;
}

}

class CompareY extends Point implements Comparator<Point>{

    @Override
    public int compare(Point o1, Point o2) {
        // TODO Auto-generated method stub
        if(o1.getY()>o2.getY())
            return 1;
        else if(o1.getY()<o2.getY())
            return -1;
        else if(o1.getX()>o2.getX())
            return 1;
        else if(o1.getX()<o2.getX())
            return -1;
        else
            return 0;

    }
}

11.

public class Test2011 {
public static void main(String[] args) {
    Scanner input=new Scanner(System.in);
    String string=input.nextLine();
    System.out.println(match(string));

}
public static boolean match(String string) {
    Stack<Character> stack=new Stack<>();
    for(int i=0;i<string.length();i++) {
        if(string.charAt(i)==')') {
            while(!stack.empty()) {
                if(stack.peek()=='(') {
                    stack.pop();
                    break;
                }
                else if(stack.peek()=='['||stack.peek()=='{')
                    return false;
                else
                    stack.pop();        
            }
        }
        else if(string.charAt(i)=='}') {
                while(!stack.empty()) {
                    if(stack.peek()=='{') {
                        stack.pop();
                        break;
                    }
                    else if(stack.peek()=='['||stack.peek()=='(')
                        return false;
                    else
                        stack.pop();        
                }
        }
        else if(string.charAt(i)==']') {
            while(!stack.empty()) {
                if(stack.peek()=='[') {
                    stack.pop();
                    break;
                }
                else if(stack.peek()=='('||stack.peek()=='{') 
                    return false;
                else
                    stack.pop();        
            }
        }
        else
            stack.push(string.charAt(i));       
    }
    if(stack.empty())
        return true;
    else
        return false;
    }

}

14.

public class Test2014 {
public static void main(String[] args) {
    Scanner input=new Scanner(System.in);
    String string=input.nextLine();
    System.out.println(post(string));
}
public static int post(String string) {
    Stack<Integer> stack=new Stack<>();
    for(int i=0;i<string.length();i++) {
        if(string.charAt(i)=='+') {
            int a1=stack.pop();
            int a2=stack.pop();
            stack.push(a1+a2);
        }
        else if(string.charAt(i)=='-') {
                int a1=stack.pop();
                int a2=stack.pop();
                stack.push(a2-a1);
            }
        else if(string.charAt(i)=='*') {
            int a1=stack.pop();
            int a2=stack.pop();
            stack.push(a2*a1);
        }
        else if(string.charAt(i)=='/') {
            int a1=stack.pop();
            int a2=stack.pop();
            stack.push(a2/a1);
        }
        else
            stack.push((int)(string.charAt(i)-'0'));
    }
    return stack.pop();

}
}

16.

    public class Test2016 {
public static void main(String[] args) {
    Scanner input= new Scanner(System.in);
    String expression =input.nextLine();
    System.out.println(infixToPostfix(expression));

}
public static String infixToPostfix(String expression) {
    String postfix="";
    Stack<Character> stack=new Stack<>();
    for(int i=0;i<expression.length();i++) {
        if(expression.charAt(i)=='(')
            stack.push(expression.charAt(i));
        else if(expression.charAt(i)=='+'||expression.charAt(i)=='-') {
            while(!stack.empty()) {
                if(stack.peek()!='(')
                    postfix+=stack.pop();

// if(stack.peek()==’+’)
// postfix+=stack.pop();
// else if(stack.peek()==’-‘)
// postfix+=stack.pop();
// else if(stack.peek()==’*’)
// postfix+=stack.pop();
// else if(stack.peek()==’/’)
// postfix+=stack.pop();
else {

                    break;
                }

            }
            stack.push(expression.charAt(i));       
        }
        else if(expression.charAt(i)=='*'||expression.charAt(i)=='/') {
            while(!stack.empty()) {
                if(stack.peek()=='*'||stack.peek()=='/')
                    postfix+=stack.pop();

                else {

                    break;
                }

            }
            stack.push(expression.charAt(i));       
        }
        else if(expression.charAt(i)==')')
            while(!stack.empty()) {
                if(stack.peek()!='(')
                    postfix+=stack.pop();
                else {
                    stack.pop();
                    break;
                }   
            }
        else {
            postfix+=expression.charAt(i);
        }



    }
    while(!stack.empty())
        postfix+=stack.pop();
    return postfix;
}

}

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