Added a function to get all permutations of a

string

mattrixwv/Algorithms.java

@@ -1,7 +1,7 @@
 //Java/JavaClasses/Algorithms.java
 //Matthew Ellison
 // Created: 03-02-19
-//Modified: 03-03-19
+//Modified: 03-24-19
 //This class holds many algorithms that I have found it useful to keep around
 //As such all of the functions in here are static and meant to be used as stand alone functions
 /*
@@ -729,6 +729,7 @@ public class Algorithms{
 		//Return the product of all elements
 		return product;
 	}
+	//This function returns true if key is found in ary
 	public static Boolean isFound(ArrayList<Integer> ary, Integer key){
 		//Look through every element in the array, looing for the key element
 		for(Integer num : ary){
@@ -762,4 +763,50 @@ public class Algorithms{
 		//If you made it to the end of the array without finding a match return false because the element was not found
 		return false;
 	}
+	//This is a function that creates all permutations of a string and returns a vector of those permutations.
+	public static ArrayList<String> getPermutations(String master){
+		return getPermutations(master, 0);
+	}
+	private static ArrayList<String> getPermutations(String master, Integer num){
+		ArrayList<String> perms = new ArrayList<String>();
+		//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 = new 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(Integer 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;
+	}
+	public static String swapString(String str, Integer first, Integer second){
+		char[] tempStr = str.toCharArray();
+		char temp = tempStr[first];
+		tempStr[first] = tempStr[second];
+		tempStr[second] = temp;
+
+		String swappedString = new String(tempStr);
+		return swappedString;
+	}
 }