.

Author: EdCharlesDiesel

Algorithms/Medium_Algorithms.Tests/UnitTest1.cs

@@ -777,10 +777,47 @@ public static bool compare(List<int> arr1, int[] arr2)
                 }
             }
             return true;
-        } 
+        }
         #endregion
 
+        #region AncestralTree
+        public Dictionary<char, AncestralTreeClass.AncestralTree> getNewTrees()
+        {
+            var trees = new Dictionary<char, AncestralTreeClass.AncestralTree>();
+            var alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+            foreach (char a in alphabet)
+            {
+                trees.Add(a, new AncestralTreeClass.AncestralTree(a));
+            }
+
+            trees['A'].AddAsAncestor(new AncestralTreeClass.AncestralTree[] {
+                  trees['B'], trees['C'], trees['D'], trees['E'], trees['F']
+                });
+            return trees;
+        }
+
+        [Fact]
+        public void AncestralTreeClassTestCase1()
+        {
+            var trees = getNewTrees();
+            trees['A'].AddAsAncestor(
+              new AncestralTreeClass.AncestralTree[] { trees['B'], trees['C'] }
+            );
+            trees['B'].AddAsAncestor(
+              new AncestralTreeClass.AncestralTree[] { trees['D'], trees['E'] }
+            );
+            trees['D'].AddAsAncestor(
+              new AncestralTreeClass.AncestralTree[] { trees['H'], trees['I'] }
+            );
+            trees['C'].AddAsAncestor(
+              new AncestralTreeClass.AncestralTree[] { trees['F'], trees['G'] }
+            );
 
+            AncestralTreeClass.AncestralTree yca =
+              AncestralTreeClass.GetYoungestCommonAncestor(trees['A'], trees['E'], trees['I']);
+            Assert.True(yca == trees['B']);
+        } 
+        #endregion
 
 
 

Algorithms/Medium_Algorithms/MediumAlgorithmsClass.cs

@@ -1610,10 +1610,84 @@ public static List<int[]> getUnvisitedNeighbors(int i, int j, int[,] matrix, boo
                 }
                 return unvisitedNeighbors;
             }
-        } 
+        }
         #endregion
 
+        #region AncestralTree
+        /// <summary>
+        /// 
+        /// </summary>
+        public class AncestralTreeClass
+        {
+            public static AncestralTree GetYoungestCommonAncestor(
+           AncestralTree topAncestor,
+           AncestralTree descendantOne,
+           AncestralTree descendantTwo
+           )
+            {
+                int depthOne = getDescendantDepth(descendantOne, topAncestor);
+                int depthTwo = getDescendantDepth(descendantTwo, topAncestor);
+                if (depthOne > depthTwo)
+                {
+                    return backtrackAncestralTree(descendantOne, descendantTwo,
+                    depthOne - depthTwo);
+                }
+                else
+                {
+                    return backtrackAncestralTree(descendantTwo, descendantOne,
+                    depthTwo - depthOne);
+                }
+            }
+
+            public static int getDescendantDepth(AncestralTree descendant, AncestralTree topAncestor)
+            {
+                int depth = 0;
+                while (descendant != topAncestor)
+                {
+                    depth++;
+                    descendant = descendant.ancestor;
+                }
+                return depth;
+            }
+
+            public static AncestralTree backtrackAncestralTree(
+                AncestralTree lowerDescendant,
+                AncestralTree higherDescendant,
+                int diff)
+            {
+                while (diff > 0)
+                {
+                    lowerDescendant = lowerDescendant.ancestor;
+                    diff--;
+                }
+                while (lowerDescendant != higherDescendant)
+                {
+                    lowerDescendant = lowerDescendant.ancestor;
+                    higherDescendant = higherDescendant.ancestor;
+                }
+                return lowerDescendant;
+            }
 
+            public class AncestralTree
+            {
+                public char name;
+                public AncestralTree ancestor;
+                public AncestralTree(char name)
+                {
+                    this.name = name;
+                    this.ancestor = null;
+                }
+                // This method is for testing only.
+                public void AddAsAncestor(AncestralTree[] descendants)
+                {
+                    foreach (AncestralTree descendant in descendants)
+                    {
+                        descendant.ancestor = this;
+                    }
+                }
+            }
+        } 
+        #endregion