Added number generators

src/main/java/com/mattrixwv/StringAlgorithms.java

@@ -0,0 +1,110 @@
+//JavaClasses/src/main/java/mattrixwv/StringAlgorithms.java
+//Matthew Ellison
+// Created: 07-03-21
+//Modified: 10-11-21
+//This class contains algorithms for strings that I've found it useful to keep around
+/*
+	Copyright (C) 2021  Matthew Ellison
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU Lesser General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU Lesser General Public License for more details.
+
+	You should have received a copy of the GNU Lesser General Public License
+	along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+package com.mattrixwv;
+
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+
+public class StringAlgorithms{
+	private StringAlgorithms(){}
+	//This is a function that creates all permutations of a string and returns a vector of those permutations.
+	public static List<String> getPermutations(String master){
+		return getPermutations(master, 0);
+	}
+	private static ArrayList<String> getPermutations(String master, int num){
+		ArrayList<String> perms = new ArrayList<>();
+		//Check if the number is out of bounds
+		if((num >= master.length()) || (num < 0)){
+			//Do nothing and return an empty arraylist
+		}
+		//If this is the last possible recurse just return the current string
+		else if(num == (master.length() - 1)){
+			perms.add(master);
+		}
+		//If there are more possible recurses, recurse with the current permutation
+		else{
+			ArrayList<String> temp = getPermutations(master, num + 1);
+			perms.addAll(temp);
+			//You need to swap the current letter with every possible letter after it
+			//The ones needed to swap before will happen automatically when the function recurses
+			for(int cnt = 1;(num + cnt) < master.length();++cnt){
+				master = swapString(master, num, (num + cnt));
+				temp = getPermutations(master, num + 1);
+				perms.addAll(temp);
+				master = swapString(master, num, (num + cnt));
+			}
+
+			//The array is not necessarily in alpha-numeric order. So if this is the full array sort it before returning
+			if(num == 0){
+				Collections.sort(perms);
+			}
+		}
+
+		//Return the arraylist that was built
+		return perms;
+	}
+	private static String swapString(String str, int first, int second){
+		char[] tempStr = str.toCharArray();
+		char temp = tempStr[first];
+		tempStr[first] = tempStr[second];
+		tempStr[second] = temp;
+
+		return new String(tempStr);
+	}
+	//This function returns the number of times the character occurs in the string
+	public static long findNumOccurrence(String str, char c){
+		return str.chars().filter(ch -> ch == c).count();
+	}
+	//Returns true if the string passed in is a palindrome
+	public static boolean isPalindrome(String str){
+		String rev = new StringBuilder(str).reverse().toString();
+		return str.equals(rev);
+	}
+	//Returns true if the string passed to it is a pandigital
+	public static boolean isPandigital(String str, char bottom, char top){
+		//Return false if top < bottom
+		if(top < bottom){
+			return false;
+		}
+
+		//Return false if the wrong number of characters are in the string
+		if(str.length() != (top - bottom + 1)){
+			return false;
+		}
+
+		//Make sure that all of the needed characters are in the string exactly one time
+		for(char cnt = bottom;cnt <= top;++cnt){
+			if(findNumOccurrence(str, cnt) != 1){
+				return false;
+			}
+		}
+
+		//If the function has reached this part it has passed all of the falsifying tests
+		return true;
+	}
+	public static boolean isPandigital(String str){
+		return isPandigital(str, '1', '9');
+	}
+}