Updated Chp.1 Solutions

Author: RodneyShag

Chp. 01 - Arrays and Strings/_1_1_Is_Unique/IsUnique.java

@@ -5,13 +5,13 @@
 // Should ask interviewer if String is ASCII or Unicode (We assume ASCII)
 
 public class IsUnique {
-    private static final int NUM_CHARS = 256; // number of ASCII characters
+    private static final int NUM_ASCII_CHARS = 256; // number of ASCII characters
 
     public static boolean uniqueCharacters(String str) {
-        if (str.length() > NUM_CHARS) {
+        if (str.length() > NUM_ASCII_CHARS) {
             return false;
         }
-        HashSet<Character> mySet = new HashSet<>(NUM_CHARS);
+        HashSet<Character> mySet = new HashSet<>(NUM_ASCII_CHARS);
         for (int i = 0; i < str.length(); i++) {
             if (mySet.contains(str.charAt(i))) {
                 return false;

Chp. 01 - Arrays and Strings/_1_4_Palindrome_Permutation/PalindromePermutation.java

@@ -3,9 +3,12 @@
 import java.util.HashMap;
 
 public class PalindromePermutation {
+    
+    private static final int NUM_LOWERCASE_LETTERS = 26;
+    
     public static boolean palPerm(String str) {
         str = str.toLowerCase().replaceAll("\\s", "");
-        HashMap<Character, Integer> map = new HashMap<>(26);
+        HashMap<Character, Integer> map = new HashMap<>(NUM_LOWERCASE_LETTERS);
         for (int i = 0; i < str.length(); i++) {
             Character ch = str.charAt(i);
             if (Character.isLetter(ch)) {
@@ -27,3 +30,6 @@ public static boolean palPerm(String str) {
         return true;
     }
 }
+
+//  Time Complexity: O(n)
+// Space Complexity: O(1)

Chp. 01 - Arrays and Strings/_1_5_One_Away/OneAway.java

@@ -25,7 +25,8 @@ private static boolean oneEditReplace(String s1, String s2) {
         return true;
     }
 
-    // Function assumes s1.length() == s2.length() + 1, that is, s1 is longer than s2 by 1 character
+    // Function assumes s1.length() == s2.length() + 1,
+    // meaning s1 is longer than s2 by 1 character
     private static Boolean oneEditInsert(String s1, String s2) {
         if (s1.length() != s2.length() + 1) {
             return null;
@@ -48,3 +49,6 @@ private static Boolean oneEditInsert(String s1, String s2) {
         return true;
     }
 }
+
+//  Time Complexity: O(n+m)
+// Space Complexity: O(1)

Chp. 01 - Arrays and Strings/_1_7_Rotate_Matrix/RotateMatrix.java

@@ -1,8 +1,5 @@
 package _1_7_Rotate_Matrix;
 
-//  Time Complexity: O(n^2). Impossible to do better since must touch all n^2 elements.
-// Space Complexity: O(1)
-
 public class RotateMatrix {
     /* Rotates square image[][] 90 degrees clockwise */
     public static void rotate90clockwise(int[][] image) {
@@ -47,3 +44,7 @@ private static void swap(int[][] image, int r1, int c1, int r2, int c2) {
         image[r2][c2] = temp;
     }
 }
+
+//  Time Complexity: O(n^2). Impossible to do better since must touch all n^2 elements.
+// Space Complexity: O(1)
+// Time/Space complexities are the same for both the 90-degree rotation and 180-degree rotation.

Chp. 01 - Arrays and Strings/_1_9_String_Rotation/StringRotation.java

@@ -9,3 +9,5 @@ public static boolean isRotation(String s1, String s2) {
         return doubledString.contains(s2);
     }
 }
+
+// Time/Space Complexities are same as .contains() function