diff --git a/Sources/AOC2018/day05.swift b/Sources/AOC2018/day05.swift
index 02d0e6a..f75db49 100644
--- a/Sources/AOC2018/day05.swift
+++ b/Sources/AOC2018/day05.swift
@@ -4,13 +4,9 @@
 
 import Foundation
 
-// Traverse the string
-// Find pairs of like letters, but opposite capitalization - < recursive? >
-// -- reduce -- and repeat
-
-
 class Reduction {
     var polymer: [Character] = []
+    var acc: [Character] = []
 
     // Supply filename for input ex: '/home/peterr/AOC2018/Sources/AOC2018/data/day05.txt'
     init(withFile filename: String) {
@@ -20,84 +16,48 @@ class Reduction {
         guard polymerString.count > 0 else { return }
         polymerString.removeLast()  // new-line
         polymer = Array(polymerString)
+        acc = Array(repeating: " ", count: polymer.count)
     }
 
     // Supply test data in the form of a String
     init(withString poly: String) {
         polymer = Array(poly)
-    }
-
-    // return an array of indicies of the first in an opposing pair
-    func getOpposites()-> [Int] {
-        var retVal: [Int] = []
-
-        if polymer.count > 1 {
-            var hit = false
-            for index in 0..<polymer.count-1 {
-                if hit {
-                    hit = false
-                } else {
-                    if (polymer[index] != polymer[index+1]) && (String(polymer[index]).lowercased() == String(polymer[index+1]).lowercased()) {
-                        hit = true
-                        retVal.append(index)
-                    }
-                }
-            }
-        }
-        return retVal
-    }
-
-    // blast the units and then "compact" the ploymer
-    func reduce(withRanges ranges: [Int]) {
-        for range in ranges {
-            polymer[range]   = " "
-            polymer[range+1] = " "
-        }
-        polymer = polymer.filter {$0 != " "}
-    }
-
-    func reducePolymer() {
-        var opp = getOpposites()
-        while opp.count > 0 {
-            reduce(withRanges: opp)
-            opp = getOpposites()
-        }
-    }
-
-    func removeUnit(withType unit: Character) {
-        for index in 0..<polymer.count {
-            if polymer[index] == unit {
-                polymer[index] = " "
+        acc = Array(repeating: " ", count: polymer.count)
+    }
+
+    func reducer() {
+        var aIdx = 0
+        acc[aIdx] = polymer[0]
+        for index in 1..<polymer.count {
+            if (aIdx > -1 && acc[aIdx] != polymer[index]) && (String(acc[aIdx]).lowercased() == String(polymer[index]).lowercased()) {
+                acc[aIdx] = " "
+                aIdx -= 1
+            } else {
+                aIdx += 1
+                acc[aIdx] = polymer[index]
             }
         }
-        let upperUnit = Character(String(unit).uppercased())
-        for index in 0..<polymer.count {
-            if polymer[index] == upperUnit {
-                polymer[index] = " "
-            }
-        }
-        polymer = polymer.filter {$0 != " "}
+        polymer = acc.filter {$0 != " "}
     }
 
     func findSmallestFullyReactedAndRemovedPolymer() -> Int {
         let start = Unicode.Scalar("a").value
         let end = Unicode.Scalar("z").value
-        let myrange = start...end
         let polyCopy = polymer
         var minLen = polymer.count
-        for i in myrange {
+        for i in start...end {
             polymer = polyCopy
+            acc = Array(repeating: " ", count: polymer.count)
             if let type = Unicode.Scalar(i) {
                 let unit = Character(type)
-                removeUnit(withType: unit)
-                reducePolymer()
+                let upperUnit = Character(String(unit).uppercased())
+                polymer = polymer.filter { $0 != unit && $0 != upperUnit }
+                reducer()
                 minLen = min(minLen, polymer.count)
             }
         }
         return minLen
     }
-
-
 }
 
 class Day05: AOCDay {
@@ -119,99 +79,55 @@ class Day05: AOCDay {
         XCTAssertEqual(test: "testReductionInit with File", withExpression: (reduc.polymer.last == "Y"))
     }
 
-    func testGetOpposites() {
-        var reduc = Reduction(withString: "aA")
-        var opp = reduc.getOpposites()
-        XCTAssertEqual(test: "testGetOpposites count", withExpression: (opp.count == 1))
-        XCTAssertEqual(test: "testGetOpposites range", withExpression: (opp == [0]))
-        reduc = Reduction(withString: "abBA")
-        opp = reduc.getOpposites()
-        XCTAssertEqual(test: "testGetOpposites count", withExpression: (opp.count == 1))
-        XCTAssertEqual(test: "testGetOpposites range", withExpression: (opp == [1]))
-        reduc = Reduction(withString: "abAB")
-        opp = reduc.getOpposites()
-        XCTAssertEqual(test: "testGetOpposites count", withExpression: (opp.count == 0))
-        reduc = Reduction(withString: "aabAAB")
-        opp = reduc.getOpposites()
-        XCTAssertEqual(test: "testGetOpposites count", withExpression: (opp.count == 0))
-        reduc = Reduction(withString: testData)
-        opp = reduc.getOpposites()
-        XCTAssertEqual(test: "testGetOpposites count", withExpression: (opp.count == 2))
-        XCTAssertEqual(test: "testGetOpposites range", withExpression: (opp == [4, 10]))
-    }
-
-    func testReduce() {
-        var reduc = Reduction(withString: "aA")
-        var opp = reduc.getOpposites()
-        reduc.reduce(withRanges: opp)
-        XCTAssertEqual(test: "testReduce count after", withExpression: (reduc.polymer.count == 0))
-        reduc = Reduction(withString: "abBA")
-        opp = reduc.getOpposites()
-        reduc.reduce(withRanges: opp)
-        XCTAssertEqual(test: "testReduce count after", withExpression: (reduc.polymer.count == 2))
-        reduc = Reduction(withString: "abAB")
-        opp = reduc.getOpposites()
-        reduc.reduce(withRanges: opp)
-        XCTAssertEqual(test: "testReduce count after", withExpression: (reduc.polymer.count == 4))
-        reduc = Reduction(withString: "aabAAB")
-        opp = reduc.getOpposites()
-        reduc.reduce(withRanges: opp)
-        XCTAssertEqual(test: "testReduce count after", withExpression: (reduc.polymer.count == 6))
-        reduc = Reduction(withString: testData)
-        opp = reduc.getOpposites()
-        reduc.reduce(withRanges: opp)
-        XCTAssertEqual(test: "testReduce count after", withExpression: (reduc.polymer.count == 12))
-    }
-
     func testReducePolymer() {
         var reduc = Reduction(withString: "aA")
-        reduc.reducePolymer()
+        reduc.reducer()
         XCTAssertEqual(test: "testReducePolymer", withExpression: (String(reduc.polymer) == ""))
         reduc = Reduction(withString: "abBA")
-        reduc.reducePolymer()
+        reduc.reducer()
         XCTAssertEqual(test: "testReducePolymer", withExpression: (String(reduc.polymer) == ""))
         reduc = Reduction(withString: "abAB")
-        reduc.reducePolymer()
+        reduc.reducer()
         XCTAssertEqual(test: "testReducePolymer", withExpression: (String(reduc.polymer) == "abAB"))
         reduc = Reduction(withString: "aabAAB")
-        reduc.reducePolymer()
+        reduc.reducer()
         XCTAssertEqual(test: "testReducePolymer", withExpression: (String(reduc.polymer) == "aabAAB"))
         reduc = Reduction(withString: testData)
-        reduc.reducePolymer()
+        reduc.reducer()
         XCTAssertEqual(test: "testReducePolymer", withExpression: (String(reduc.polymer) == "dabCBAcaDA"))
     }
 
     func testRemoveUnit() {
         var reduc = Reduction(withString: testData)
-        reduc.removeUnit(withType: "a")
+        reduc.polymer = reduc.polymer.filter { $0 != "a" && $0 != "A" }
         XCTAssertEqual(test: "testRemoveOneType", withExpression: (String(reduc.polymer) == "dbcCCBcCcD"))
         reduc = Reduction(withString: testData)
-        reduc.removeUnit(withType: "b")
+        reduc.polymer = reduc.polymer.filter { $0 != "b" && $0 != "B" }
         XCTAssertEqual(test: "testRemoveOneType", withExpression: (String(reduc.polymer) == "daAcCaCAcCcaDA"))
         reduc = Reduction(withString: testData)
-        reduc.removeUnit(withType: "c")
+        reduc.polymer = reduc.polymer.filter { $0 != "c" && $0 != "C" }
         XCTAssertEqual(test: "testRemoveOneType", withExpression: (String(reduc.polymer) == "dabAaBAaDA"))
         reduc = Reduction(withString: testData)
-        reduc.removeUnit(withType: "d")
+        reduc.polymer = reduc.polymer.filter { $0 != "d" && $0 != "D" }
         XCTAssertEqual(test: "testRemoveOneType", withExpression: (String(reduc.polymer) == "abAcCaCBAcCcaA"))
     }
 
     func testRemoveAndReact() {
         var reduc = Reduction(withString: testData)
-        reduc.removeUnit(withType: "a")
-        reduc.reducePolymer()
+        reduc.polymer = reduc.polymer.filter { $0 != "a" && $0 != "A" }
+        reduc.reducer()
         XCTAssertEqual(test: "testRemoveAndReact a", withExpression: (String(reduc.polymer) == "dbCBcD"))
         reduc = Reduction(withString: testData)
-        reduc.removeUnit(withType: "b")
-        reduc.reducePolymer()
+        reduc.polymer = reduc.polymer.filter { $0 != "b" && $0 != "B" }
+        reduc.reducer()
         XCTAssertEqual(test: "testRemoveAndReact b", withExpression: (String(reduc.polymer) == "daCAcaDA"))
         reduc = Reduction(withString: testData)
-        reduc.removeUnit(withType: "c")
-        reduc.reducePolymer()
+        reduc.polymer = reduc.polymer.filter { $0 != "c" && $0 != "C" }
+        reduc.reducer()
         XCTAssertEqual(test: "testRemoveAndReact c", withExpression: (String(reduc.polymer) == "daDA"))
         reduc = Reduction(withString: testData)
-        reduc.removeUnit(withType: "d")
-        reduc.reducePolymer()
+        reduc.polymer = reduc.polymer.filter { $0 != "d" && $0 != "D" }
+        reduc.reducer()
         XCTAssertEqual(test: "testRemoveAndReact d", withExpression: (String(reduc.polymer) == "abCBAc"))
     }
 
@@ -223,8 +139,6 @@ class Day05: AOCDay {
 
     func day05Tests() {
         testReductionInit()
-        testGetOpposites()
-        testReduce()
         testReducePolymer()
         testRemoveUnit()
         testRemoveAndReact()
@@ -232,13 +146,10 @@ class Day05: AOCDay {
     }
 
     func day05Final() {
-        // var reduc = Reduction(withFile: "/home/peterr/AOC2018/Sources/AOC2018/data/day05.txt")
-        // Run test data as the real data takes too long
-        var reduc = Reduction(withString: testData)
-        reduc.reducePolymer()
+        var reduc = Reduction(withFile: "/home/peterr/AOC2018/Sources/AOC2018/data/day05.txt")
+        reduc.reducer()
         print("Answer to part 1 is: \(reduc.polymer.count)")
-        // reduc = Reduction(withFile: "/home/peterr/AOC2018/Sources/AOC2018/data/day05.txt")
-        reduc = Reduction(withString: testData)
+        reduc = Reduction(withFile: "/home/peterr/AOC2018/Sources/AOC2018/data/day05.txt")
         let answer = reduc.findSmallestFullyReactedAndRemovedPolymer()
         print("Answer to part 2 is: \(answer)")
     }