From 5e2d87a029be4a4c1c2e826e7548a8e33a782fc2 Mon Sep 17 00:00:00 2001
From: Matthew Ellison <m_ellison@ymail.com>
Date: Mon, 25 Mar 2019 12:30:32 -0400
Subject: [PATCH] Added a function to return all permutations of a string

---
 Algorithms.lua | 77 ++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 75 insertions(+), 2 deletions(-)

diff --git a/Algorithms.lua b/Algorithms.lua
index 1ab83fc..f35b7ab 100644
--- a/Algorithms.lua
+++ b/Algorithms.lua
@@ -1,7 +1,7 @@
 --luaClasses/Algorithms.lua
 --Matthew Ellison
--- Created: 2-4-19
---Modified: 2-7-19
+-- Created: 02-04-19
+--Modified: 03-24-19
 --This is a file of algorithms that I have found it useful to keep around at all times
 
 
@@ -191,3 +191,76 @@ function getProd(ary)
 	--Return the product of all elements
 	return prod;
 end
+
+function getPermutations(master, num)
+	--If no num was given make it 0
+	local num = num or 1
+	local perms = {};
+	--Check if the number is out of bounds
+	if((num > string.len(master)) or (num < 0)) then
+		--Do nothing and return an empty list
+		perms = {};
+	--If this is the last possible recurse just return the current string
+	elseif(num == string.len(master)) then
+		perms[#perms + 1] = master;
+	--If there are more possible recurses, recurse with the current permutations
+	else
+		local temp = getPermutations(master, num + 1);
+		--Add the elements of temp to perms
+		for loc = 1, #temp do
+			perms[#perms + 1] = temp[loc]
+		end
+		--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 cnt = 1, (string.len(master) - num) do
+
+			--Swap two elements
+			--Turn it into byte array so you can change values
+			local tempStr = {};
+			for loc = 1, #master do
+				tempStr[loc] = string.byte(master:sub(loc, loc));
+			end
+
+			--Swap the two elements
+			local tempChar = tempStr[num];
+			tempStr[num] = tempStr[num + cnt];
+			tempStr[num + cnt] = tempChar;
+			--Change it back to a string
+			master = "";
+			for loc = 1, #tempStr do
+				master = master .. string.char(tempStr[loc]);
+			end
+
+			--Get the permutations after swapping two elements
+			temp = getPermutations(master, num + 1);
+			--Add the elements of temp to perms
+			for loc = 1, #temp do
+				perms[#perms + 1] = temp[loc]
+			end
+
+			--Swap the elements back
+			--Turn it into byte array so you can change values
+			tempStr = {};
+			for loc = 1, #master do
+				tempStr[loc] = string.byte(master:sub(loc, loc));
+			end
+			--Swap the two elements
+			tempChar = tempStr[num];
+			tempStr[num] = tempStr[num + cnt];
+			tempStr[num + cnt] = tempChar;
+			--Change it back to a string
+			master = "";
+			for loc = 1, #tempStr do
+				master = master .. string.char(tempStr[loc]);
+			end
+		end
+	end
+
+	--The array is not necessarily in alpha-numeric order. So if this is the full array sort it before returning
+	if(num == 1) then
+		table.sort(perms);
+	end
+
+	--Return the list
+	return perms;
+end