Problem 01 - Ch 05

README.md

@@ -45,7 +45,7 @@ Java Solutions for Cracking the Coding Interview - 6th Edition
 - [X] [12 - Paths with Sum](../master/src/com/deepak/ctci/Ch04_Trees_And_Graphs/Problem_12.java)
 
 **Ch 05 - Bit Manipulation**  
-- [ ] 01 - Insertion
+- [X] [01 - Insertion](../master/src/com/deepak/ctci/Ch05_Bit_Manipulation/Problem_01.java)
 - [ ] 02 - Binary to String
 - [ ] 03 - Flip Bit to Win
 - [ ] 04 - Next Number

src/com/deepak/ctci/Ch05_Bit_Manipulation/Problem_01.java

@@ -23,13 +23,35 @@
  * @author Deepak
  */
 public class Problem_01 {
-
-	public int mergeMIntoN(int M, int N, int i, int j) {
-		if (i < 0 || i >= 32 || j < i) {
+
+	/**
+	 * Method to merge M into N
+	 * 
+	 * @param N
+	 * @param M
+	 * @param i
+	 * @param j
+	 * @return {@link int}
+	 */
+	public static int mergeMIntoN(int N, int M, int i, int j) {
+		/* Since we are dealing with 32 bits, 
+		 * i and j can't be greater then 32 */
+		if (i > 32 || i > j) {
 			return 0;
 		}
-
-		return 0;
+		/* We need to clear the bits from i to j.
+		 * For that, we need a mask. Let's take all 1's
+		 * and keep only those 1, where M can fit in, rest
+		 * can be made 0 */
+		int allOnes = ~0;
+		int left = allOnes << (j + 1);
+		int right = ((1 << i) - 1);
+		int mask = left | right;
+
+		/* Clear i through j */
+		int n_cleared = N & mask;
+		int m_shifted = M << i;
+		return n_cleared | m_shifted;
 	}
 
 }

src/com/deepak/ctci/Library/HelperMethods.java

@@ -37,5 +37,27 @@ public static int randomIntInRange(int min, int max) {
 		Random random = new Random();
 		return random.nextInt(max + 1 - min) + min;
 	}
+
+	/**
+	 * Method to print a full binary string
+	 * 
+	 * @param input
+	 * @return {@link String}
+	 */
+	public static String toFullBinaryString(int input, int numberOfBits) {
+		StringBuilder builder = new StringBuilder();
+		/* Create a display mask on the last bit */
+		int displayMask = 1 << (numberOfBits - 1);
+		/* Loop through all the bits and print accordingly */
+		for (int bit = 1; bit <= numberOfBits; bit++) {
+			builder.append((input & displayMask) == 0 ? '0' : '1');
+			input <<= 1;
+			/* Create space after 4 bits */
+			if ((bit % 4) == 0) {
+				builder.append(' ');
+			}
+		}
+		return builder.toString().trim();
+	}
 
 }

test/com/deepak/ctci/Ch05_Bit_Manipulation/Problem_01_Test.java

@@ -0,0 +1,31 @@
+/**
+ * Cracking-The-Coding-Interview
+ * Problem_01_Test.java
+ */
+package com.deepak.ctci.Ch05_Bit_Manipulation;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.deepak.ctci.Library.HelperMethods;
+
+/**
+ * Test cases for Problem 01
+ * 
+ * @author Deepak
+ */
+public class Problem_01_Test {
+
+	/**
+	 * Method to test merging of bits from M to N
+	 */
+	@Test
+	public void testMergeOfBits() {
+		int N = 103217;
+		int M = 13;
+		Assert.assertEquals(HelperMethods.toFullBinaryString(N, 32), "0000 0000 0000 0001 1001 0011 0011 0001");
+		Assert.assertEquals(HelperMethods.toFullBinaryString(M, 32), "0000 0000 0000 0000 0000 0000 0000 1101");
+		Assert.assertEquals(HelperMethods.toFullBinaryString(Problem_01.mergeMIntoN(103217, 13, 4, 12), 32), "0000 0000 0000 0001 1000 0000 1101 0001");
+	}
+
+}