UnionFind

adagio · adagio · commit 40fcc0a7ffe7 · 2017-04-10T15:34:37.000-05:00
diff --git a/Pages/UnionFind.xcplaygroundpage/Contents.swift b/Pages/UnionFind.xcplaygroundpage/Contents.swift
@@ -0,0 +1,64 @@
+//: [Previous](@previous)
+
+import Foundation
+
+var dsu = UnionFind<Int>()
+
+for i in 1...10 {
+    dsu.addSetWith(i)
+}
+// now our dsu contains 10 independent sets
+// let's divide our numbers into two sets by divisibility by 2
+for i in 3...10 {
+    if i % 2 == 0 {
+        dsu.unionSetsContaining(2, and: i)
+    } else {
+        dsu.unionSetsContaining(1, and: i)
+    }
+}
+
+print(dsu.inSameSet(2, and: 4))
+print(dsu.inSameSet(4, and: 6))
+print(dsu.inSameSet(6, and: 8))
+print(dsu.inSameSet(8, and: 10))
+
+print(dsu.inSameSet(1, and: 3))
+print(dsu.inSameSet(3, and: 5))
+print(dsu.inSameSet(5, and: 7))
+print(dsu.inSameSet(7, and: 9))
+
+print(dsu.inSameSet(7, and: 4))
+print(dsu.inSameSet(3, and: 6))
+
+
+var dsuForStrings = UnionFind<String>()
+let words = ["all", "border", "boy", "afternoon", "amazing", "awesome", "best"]
+
+dsuForStrings.addSetWith("a")
+dsuForStrings.addSetWith("b")
+
+// In that example we divide strings by its first letter
+for word in words {
+    dsuForStrings.addSetWith(word)
+    if word.hasPrefix("a") {
+        dsuForStrings.unionSetsContaining("a", and: word)
+    } else if word.hasPrefix("b") {
+        dsuForStrings.unionSetsContaining("b", and: word)
+    }
+}
+
+
+
+print(dsuForStrings.inSameSet("a", and: "all"))
+print(dsuForStrings.inSameSet("all", and: "awesome"))
+print(dsuForStrings.inSameSet("amazing", and: "afternoon"))
+
+print(dsuForStrings.inSameSet("b", and: "boy"))
+print(dsuForStrings.inSameSet("best", and: "boy"))
+print(dsuForStrings.inSameSet("border", and: "best"))
+
+print(dsuForStrings.inSameSet("amazing", and: "boy"))
+print(dsuForStrings.inSameSet("all", and: "border"))
+
+
+//: [Next](@next)
diff --git a/Pages/UnionFind.xcplaygroundpage/Sources/UnionFind.swift b/Pages/UnionFind.xcplaygroundpage/Sources/UnionFind.swift
@@ -0,0 +1,58 @@
+import Foundation
+
+public struct UnionFind<T: Hashable> {
+    
+    private var index = [T: Int]()
+    private var parent = [Int]()
+    private var size = [Int]()
+    
+    public init() {}
+    
+    public mutating func addSetWith(_ element: T) {
+        index[element] = parent.count
+        parent.append(parent.count)
+        size.append(1)
+    }
+    
+    public mutating func setOf(_ element: T) -> Int? {
+        if let indexOfElement = index[element] {
+            return setByIndex(indexOfElement)
+        } else {
+            return nil
+        }
+    }
+    
+    // search up to root
+    private mutating func setByIndex(_ index: Int) -> Int {
+        if parent[index] == index {  // 1
+            return index
+        } else {
+            parent[index] = setByIndex(parent[index])  // 2
+            return parent[index]       // 3
+        }
+    }
+    
+    // easy
+    public mutating func inSameSet(_ firstElement: T, and secondElement: T) -> Bool {
+        if let firstSet = setOf(firstElement), let secondSet = setOf(secondElement) {
+            return firstSet == secondSet
+        } else {
+            return false
+        }
+    }
+    
+    public mutating func unionSetsContaining(_ firstElement: T, and secondElement: T) {
+        if let firstSet = setOf(firstElement), let secondSet = setOf(secondElement) {  // 1
+            if firstSet != secondSet {               // 2
+                if size[firstSet] < size[secondSet] {  // 3
+                    parent[firstSet] = secondSet         // 4
+                    size[secondSet] += size[firstSet]    // 5
+                } else {
+                    parent[secondSet] = firstSet
+                    size[firstSet] += size[secondSet]
+                }
+            }
+        }
+    }
+    
+}
diff --git a/contents.xcplayground b/contents.xcplayground
@@ -5,5 +5,6 @@
         <page name='Stack'/>
         <page name='Linked List'/>
         <page name='Trees'/>
+        <page name='UnionFind'/>
     </pages>
 </playground>
diff --git a/playground.xcworkspace/xcuserdata/francocedillo.xcuserdatad/UserInterfaceState.xcuserstate b/playground.xcworkspace/xcuserdata/francocedillo.xcuserdatad/UserInterfaceState.xcuserstate
diff --git a/xcuserdata/francocedillo.xcuserdatad/xcdebugger/Breakpoints_v2.xcbkptlist b/xcuserdata/francocedillo.xcuserdatad/xcdebugger/Breakpoints_v2.xcbkptlist
@@ -2,4 +2,22 @@
 <Bucket
    type = "1"
    version = "2.0">
+   <Breakpoints>
+      <BreakpointProxy
+         BreakpointExtensionID = "Xcode.Breakpoint.FileBreakpoint">
+         <BreakpointContent
+            shouldBeEnabled = "Yes"
+            ignoreCount = "0"
+            continueAfterRunningActions = "No"
+            filePath = "Algorithms.playground/Pages/UnionFind.xcplaygroundpage/Sources/UnionFind.swift"
+            timestampString = "513547899.06388"
+            startingColumnNumber = "9223372036854775807"
+            endingColumnNumber = "9223372036854775807"
+            startingLineNumber = "18"
+            endingLineNumber = "18"
+            landmarkName = "setOf(_:)"
+            landmarkType = "7">
+         </BreakpointContent>
+      </BreakpointProxy>
+   </Breakpoints>
 </Bucket>
