p1.java

import java.lang.StringIndexOutOfBoundsException;
import java.util.Scanner;

public class Palindrome {
    // Part 1
    // O(n)
    public static boolean palindromeIterative(String input) {
        // filter text so it only contains lowercase letters and numbers
        input = input.toLowerCase().replaceAll("[^a-z0-9]", "");
        // pairs the first half to the second half, so we only
        // need to iterate n/2 times
        // personally I like this method more
        int n = input.length();
        for (int i=0; i<n/2; i++) {
            if (input.charAt(i) != input.charAt(n-i-1)) return false;
        }
        return true;
    }
    
    // O(n)
    public static boolean palindromeRecursive(String input) {
        input = input.toLowerCase().replaceAll("[^a-z0-9]", "");
        // this is kind of self explanatory, checks if the two edges match,
        // and recurses all the stuff in the middle
        int n = input.length();
        if (n <= 1) return true;
        if (input.charAt(0) != input.charAt(n-1)) return false;
        return palindromeRecursive(input.substring(1, n-1));
    }
    
    
    
    // Part 2
    public static boolean anagramChecker(String x, String y) {
        x = x.toLowerCase().replaceAll("[^a-z0-9]", "");
        y = y.toLowerCase().replaceAll("[^a-z0-9]", "");
        
        /**
         * personally I would just break the strings into char arrays,
         * sort, then compare... I don't think that's what the professor
         * intended for this assignment though, so I'm just going to
         * count how many times each letter appears in the first one, then
         * subtract with the letters in the last one.
         * we'll know they're anagrams if it results in an all zero'd out array
         **/
        int count[] = new int[36]; // 26 + 10
        // we count the instances of each letter
        for (int i=0; i<x.length(); i++) {
            // if it's a letter... otherwise it's a number
            int index = -1;
            if (x.charAt(i) >= 'a') index = x.charAt(i)-'a';
            else index = x.charAt(i)-'0'+26;
            count[index]++;
        }
        // now we decrement >:3
        for (int i=0; i<y.length(); i++) {
            int index = -1;
            if (y.charAt(i) >= 'a') index = y.charAt(i)-'a';
            else index = y.charAt(i)-'0'+26;
            count[index]--;
        }
        // if it's nonzero at any point, we've either undercounted or overcounted a letter
        for (int i=0; i<36; i++) if (count[i] != 0) return false;
        return true;
    }
    
    public static String addSubstring(String input, String substring, int index) {
        /**
         * i asked the discord if we need to handle errors...
         * i don't know why they didn't put anything about error handling in the
         * assignment sheet, but i'm not about to get points off for something
         * silly like missing this
         * 
         * substring the part before, add the letter, then substring the part after
         **/
        if (index > input.length()) throw new StringIndexOutOfBoundsException("Index is too big for this string");
        return input.substring(0, index) + substring + input.substring(index, input.length());
    }
    
    public static int getLength(String input) {
        // cmon.
        return input.length();
    }
    
    public static int occurrenceCounter(String input, String substring) {
        /**
         * consider that "aaa" contains two occurances of "aa"
         * occurances may overlap, so we only do (index+1) when
         * we use indexOf instead of (index+substring.length())
         **/
        int index = -1;
        int occurances = 0;
        do {
            index = input.indexOf(substring, index+1);
            if (index != -1) occurances++;
        } while (index != -1);
        return occurances;
    }
    
    public static String sentenceReversal(String input) {
        // in Javascript this would just be input.split(" ").reverse().join(" ")
        // i don't think I'm allowed to use ArrayLists, so whatever
        char lastLetter = input.charAt(input.length()-1);
        if (lastLetter == '.' || lastLetter == '?') {
            // remove last letter from string, we'll add the end punctuation later
            input = input.substring(0, input.length()-1);
        } else {
            // otherwise set to null char
            lastLetter = 0;
        }
        
        String[] words = input.split(" ");
        String result = "";
        for (int i=0; i<words.length; i++) {
            result += words[words.length-i-1];
            if (i < words.length-1) result += " ";
        }
        if (lastLetter != 0) result += lastLetter;
        
        return result;
    }
    
    // Additional Requirements
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        System.out.println("Welcome to the App\n\t1. Palindrome Check\n\t2. Anagram Check\n\t3. Add Substring\n\t4. Get Length\n\t5. Count Occurances\n\t6. Reverse Sentence\n\t7. Quit");
        int option = -1;
        while (option != 7) {
            System.out.print("Choose an option: ");
            option = sc.nextInt();
            System.out.println("");
            
            switch (option) {
                case 1: {
                    System.out.println("String?");
                    // after consuming an int, you need to consume an empty line to take in a new line
                    sc.nextLine();
                    String a = sc.nextLine();
                    System.out.println("\nOutput: " + palindromeIterative(a));
                    break;
                }
                case 2: {
                    System.out.println("String?");
                    sc.nextLine();
                    String a = sc.nextLine();
                    System.out.println("String?");
                    String b = sc.nextLine();
                    System.out.println("\nOutput: " + anagramChecker(a, b));
                    break;
                }
                case 3: {
                    System.out.println("String?");
                    sc.nextLine();
                    String a = sc.nextLine();
                    System.out.println("Substring?");
                    String b = sc.nextLine();
                    int c = sc.nextInt();
                    System.out.println("\nOutput: " + addSubstring(a, b, c));
                    break;
                }
                case 4: {
                    System.out.println("String?");
                    sc.nextLine();
                    String a = sc.nextLine();
                    System.out.println("\nOutput: " + getLength(a));
                    break;
                }
                case 5: {
                    System.out.println("String?");
                    sc.nextLine();
                    String a = sc.nextLine();
                    System.out.println("Substring?");
                    String b = sc.nextLine();
                    System.out.println("\nOutput: " + occurrenceCounter(a, b));
                    break;
                }
                case 6: {
                    System.out.println("String?");
                    sc.nextLine();
                    String a = sc.nextLine();
                    System.out.println("\nOutput: " + sentenceReversal(a));
                    break;
                }
                case 7: {
                    break;
                }
                default: {
                    System.out.println("Unknown option, choose again");
                }
                System.out.println("");
            }
        }
        System.out.println("\nHave a nice day :3");
    }
}