【第五天打卡。

Bag Sample

Compute the average and simple standard deviation of the double values on standard input

public class Stats {
    public static void main (String[] args) {
        Bag<Double> numbers = new Bag<Double>();
        while(!StdIn.isEmpty) 
            numbers.add(StdIn.readDouble());
        int N = numbers.size();
        double sum = 0.0;
        for (double x : numbers)
            sum += x;
        double mean = sum/N;
        sum = 0.0;
        for (double x : numbers)
            sum += (x-mean)*(x-mean);
        double std = Math.sqrt(sum/(N-1));
        StdOut.printf("Mean: %.2f\n", mean);
        StdOut.printf("Std dev: %.2f\n", std);
 
    }
}

FIFO Queues

Sample queue client

public static int[] readInts (String name) {
    In in = new In(name);
    Queue<Integer> q = new Queue<Integer>();
    while(!in.isEmpty()) 
        q.enqueue(in.readInt());
    int N = q.size();
    int[] a = new int[N];
    for(int i = 0; i < N; i++) 
        a[i] = q.dequeue();
    return a;
}

LIFO Stacks

Sample stack client

public class Reverse {
    public static void main (String[] args) {
        Stack<Integer> stack = new Stack<Integer>();
        while(!StdIn.isEmpty()) 
            stack.push(StdIn.readIn());
        for(int i : stack)
            StdOut.println(i);
    }
}

Dijkstra's Two-Stack Algorithm for Expression Evaluation

public class evaluate {
    public static void main(String[] args) {
        Stack<String> ops = new Stack<String>();
        Stack<Double> vals = new Stack<Double>();
        while (!StdIn.isEmpty){
            String s = StdIn.readString();
            if (s.equals("("));
            else if (s.equals("+"))    ops.push(s);
            else if (s.equals("-"))     ops.push(s);
            else if (s.equals("*"))    ops.push(s);
            else if (s.equals("/"))     ops.push(s);
            else if (s.equals(")"))     ops.push(s);
            else if (s.equals("sqrt")) ops.push(s);
            else if (s.equals(")")) {
                String op = ops.pop();
                Double v = vals.pop();
                if (op.equals("+"))    v = vals.pop() + v;
                else if (op.equals("-")) v = vals.pop() - v;
                else if (op.equals("*")) v = vals.pop() * v;
                else if (op.equals("/")) v = vals.pop() / v;
                else if (op.equals("sqrt")) v = Math.sqrt(v);
                vals.push(v);
            }
            else vals.push(Double.parseDouble(s));
        }
        StdOut.println(vals.pop());
    }    
}