Merge pull request ashutosh97#88 from plaidshirtakos/master

Reverse a string in place and Rod cutting problems are added

Author: ashutosh97

Reverse string in place/question.txt

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+Write a program to reverse a String in place in Java, without using additional memory.
+You cannot use any library classes or methods like e.g. StringBuilder to solve this problem. This restriction is placed because StringBuilder and StringBuffer class define a reverse() method which can easily reverse the given String.

Reverse string in place/solution.java

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+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Java Program to reverse a String in place, 
+ * without any additional buffer in Java.
+ *
+ * @author WINDOWS 8
+ *
+ */
+public class StringReversal {
+
+    /**
+     * Java method to reverse a String in place
+     * @param str 
+     * @return  reverse of String
+     */
+    public static String reverse(String str) {
+        if(str == null || str.isEmpty()){
+            return str;
+        }
+        char[] characters = str.toCharArray();
+        int i = 0;
+        int j = characters.length - 1;
+        while (i < j) {
+            swap(characters, i, j);
+            i++;
+            j--;
+        }
+        return new String(characters);
+    }
+
+    /**
+     * Java method to swap two numbers in given array
+     * @param str
+     * @param i
+     * @param j 
+     */
+    private static void swap(char[] str, int i, int j) {
+        char temp = str[i];
+        str[i] = str[j];
+        str[j] = temp;
+    }
+
+    @Test
+    public void reverseEmptyString(){
+        Assert.assertEquals("", reverse(""));
+    }
+    
+    @Test
+    public void reverseString(){
+        Assert.assertEquals("cba", reverse("abc"));
+    }
+    
+    @Test
+    public void reverseNullString(){
+        Assert.assertEquals(null, reverse(null));
+    }
+    
+    @Test
+    public void reversePalindromeString(){
+        Assert.assertEquals("aba", reverse("aba"));
+    }
+    
+    @Test
+    public void reverseSameCharacterString(){
+        Assert.assertEquals("aaa", reverse("aaa"));
+    }
+    
+    @Test
+    public void reverseAnagramString(){
+        Assert.assertEquals("mary", reverse("yram"));
+    }
+}

Rod cutting problem/question.txt

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+Given a rod of length n, and an array that contains the prices of all the pieces smaller than n, determine the maximum profit you could obtain from cutting up the rod and selling its pieces.

Rod cutting problem/solution.java

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+class rod_cutting
+{
+  static int cut_rod(int price[], int n)
+  {
+    // Declaring a 2D array, T
+    int T[][] = new int[n-1][n+1];
+
+    // Initializing the array to all zeros
+    for(int i=0; i < n-1; i++)
+    {
+      for(int j=0; j < n+1; j++ )
+      {
+        T[i][j] = 0;
+      }
+    }
+
+    for(int i=0; i < n-1; i++)
+    {
+      for(int j=0; j < n+1; j++ )
+      {
+        // First column => 0 length of rod => 0 profit
+        if(j == 0) {
+          continue;
+        }
+
+        // First row => T[i-1][j] doesn't exist so just pick the second value
+        else if(i == 0) {
+          T[i][j] = price[i] + T[i][j-i-1];
+        }
+
+        // where j <= i => T[i][j-i-1] doesn't exist so just pick the first value
+        else if(j-i-1 < 0) {
+          T[i][j] = T[i-1][j];
+        }
+
+        // using the whole expression
+        else {
+          T[i][j] = Math.max(T[i-1][j], (price[i] + T[i][j-i-1]));
+        }
+      }
+    }
+    return T[n-2][n];
+  }
+
+  public static void main(String args[]) 
+  { 
+     int price[] = new int[] {2,5,7,8}; 
+     int n = 5;
+     System.out.println("Maximum profit is " + cut_rod(price, n)); 
+    } 
+}