Exam 2 Review Code

Fib.java

package source;

public class Fib {
	public static void main(String[] args) {
		System.out.println("Total paths given 4 tiles "+countPaths(4));
		
		System.out.println(intPower(2, 16));
	}
	
	public static void start(int n ){
		
		for (int i=n; i >= 0; i--){
			String line = "";
			for (int j=0; j < i; j++){
				line += " ";
			}
			line += "*";
			System.out.println(line);
		}
	}
	
	public static int intPower(int x, int p) {
		if (p <= 0){
			return 1;
		}
		
		if (p % 2 == 0){
			int result = intPower(x, p/2);
			return result * result;
		}
		
		if (p % 2 != 0){
			 return x * intPower(x, p-1);
		}
		
		return 0;
	}
	
	public static int countPaths(int n) {
		// Case in which we have a valid path
		if (n == 1)
			return 1;
		
		// Case in which we have an invalid path
		if (n < 1)
			return 0;
		
		// Count the number of valid paths for the remaining steps
		int totalPaths = 0;
		totalPaths += countPaths(n-1);
		totalPaths += countPaths(n-2);
		totalPaths += countPaths(n-3);
		return totalPaths;
		
		//return countPaths(n-1)+countPaths(n-2)+countPaths(n-3);
	}
	
	public static int fib(int n) {
		if (n == 0){
			return 0;
		}
		if (n == 1){
			return 1;
		}
		
		if (n > 1) {
		return fib(n-1) + fib(n-2);
		} else {
			return -1;
		}
	}
}

FileIo.java

package source;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;

public class FileIo {
	public static void main (String[] args) throws FileNotFoundException {
		
		System.out.print("Enter filename > ");
		Scanner in = new Scanner(System.in);
		String filename = in.next();
		
		File inFile = new File(filename);
	
		System.out.println(filename);
		File outFile = new File(filename+".out");
		
		Scanner inFileScanner = new Scanner(inFile);
		PrintWriter outFileWriter = new PrintWriter(outFile);
		
		while (inFileScanner.hasNextLine()) {
			String line = inFileScanner.nextLine(); // this is also a comment
			
			// this is a comment
			if (!line.trim().startsWith("//")){
				 String newLine = line.split("//")[0];
				 outFileWriter.write(newLine+"\n");
			}
		}
		
		System.out.println("Done! Written to "+filename+".out");
		inFileScanner.close();
		outFileWriter.close();
	}
	
	

}

Mergin.java

package soruce;

import java.util.Arrays;

public class Mergin {
	
	public static void main (String[] args) {
		int[] arr = {3 ,4 ,2 ,-1 ,0, 10, -5};
		mergeSort(arr);
		
		System.out.println(Arrays.toString(arr));
		
		//[-5, -1, 0, 2, 3, 4, 10]
	}
	
	public static void mergeSort(int[] arr)
	{
		mergeSortRec(arr, 0, arr.length - 1);
	}
	
	public static void mergeSortRec(int[] arr, int start, int end) {
		
		//int mid = (start + end) / 2;
	    //  int leftSum = arraySum(arr, start, mid);
	    //  int rightSum = arraySum(arr, mid + 1, end);
		
		if (start == end)
			return;
		
		int mid = (start + end) / 2;
		mergeSortRec(arr, start, mid);
		mergeSortRec(arr, mid + 1, end);
		
		merge(arr, start, end, mid);
	}
	
	public static void merge(int[] arr, int start, int end, int mid) {
	    
	    // copy first half of arr to a temporary array
	    int aSize = mid - start + 1;
	    int[] a = new int[aSize];
	    for (int i = 0; i < aSize; ++i)
	    {
	      a[i] = arr[i + start];
	    }
	    int[] b = arr;                // 'b' array is just the second half of arr
	    int[] result = arr;           // result goes in original array arr
	    
	    int i = 0;                    // starting index in a
	    int j = mid + 1;              // starting index in b
	    final int iMax = aSize;       // 1 + max index in a
	    final int jMax = end + 1;     // 1 + max index in b
	    int k = start;                // index in result
	    
	    // Remaining code is identical to previous version MergeSort.merge()
	    
	    while (i < iMax && j < jMax)
	    {
	      if (a[i] <= b[j])
	      {
	        result[k] = a[i];
	        i = i + 1;
	        k = k + 1;
	       }
	      else
	      {
	        result[k] = b[j];
	        j = j + 1;
	        k = k + 1;
	      }
	    }
	    
	    // pick up any stragglers
	    while (i < iMax)
	    {
	      result[k] = a[i];
	      i = i + 1;
	      k = k + 1;
	    }
	    while (j < jMax)
	    {
	      result[k] = b[j];
	      j = j + 1;
	      k = k + 1;
	    }    
	  }
}

WrapperClasses.java

package soruce;

import java.util.ArrayList;

public class WrapperClasses {
	public static void main(String[] args) {
		int a = 15;
		Integer b = 30;
		Integer c = new Integer(30);
		Integer d = b;
		
		ArrayList<Integer> arr = new ArrayList<Integer>();
		arr.add(5);
		arr.add(a);
		arr.add(b);
		
		b.toString();
	}
}