17.18: Some code cleanup + adding new solution for problem

Author: Gayle McDowell

Java/Ch 17. Hard/Q17_18_Shortest_Supersequence/QuestionA.java

@@ -37,6 +37,9 @@ public static Range shortestSupersequence(int[] bigArray, int[] smallArray) {
 				bestEnd = end;
 			}
 		}
+		if (bestStart < 0 || bestEnd < 0) {
+			return null;
+		}
 		return new Range(bestStart, bestEnd);
 	}
 

Java/Ch 17. Hard/Q17_18_Shortest_Supersequence/QuestionB.java

@@ -60,6 +60,9 @@ public static Range getShortestClosure(int[] closures) {
 				bestEnd = closures[i];
 			}
 		}
+		if (bestStart < 0 || bestEnd < 0) {
+			return null;
+		}
 		return new Range(bestStart, bestEnd);
 	}
 

Java/Ch 17. Hard/Q17_18_Shortest_Supersequence/QuestionC.java

@@ -2,6 +2,20 @@
 
 public class QuestionC {
 
+	public static Range shortestSupersequence(int[] big, int[] small) {
+		int[] closures = getClosures(big, small);
+		return getShortestClosure(closures);
+	}
+	
+	/* Get closure for each index. */
+	public static int[] getClosures(int[] big, int[] small) {
+		int[] closure = new int[big.length];
+		for (int i = 0; i < small.length; i++) {
+			sweepForClosure(big, closure, small[i]);
+		}
+		return closure;
+	}	
+	
 	/* Do backwards sweep and update the closures list with the next occurrence of value, if it's later than the current closure*/
 	public static void sweepForClosure(int[] big, int[] closures, int value) {
 		int next = -1;
@@ -15,17 +29,9 @@ public static void sweepForClosure(int[] big, int[] closures, int value) {
 		}
 	}
 
-	/* Get closure for each index. */
-	public static int[] getClosures(int[] big, int[] small) {
-		int[] closure = new int[big.length];
-		for (int i = 0; i < small.length; i++) {
-			sweepForClosure(big, closure, small[i]);
-		}
-		return closure;
-	}
-	
 	/* Get shortest closure. */
 	public static Range getShortestClosure(int[] closures) {
+		if (closures == null || closures.length == 0) return null;
 		Range shortest = new Range(0, closures[0]);
 		for (int i = 1; i < closures.length; i++) {
 			if (closures[i] == -1) {
@@ -36,20 +42,20 @@ public static Range getShortestClosure(int[] closures) {
 				shortest = range;
 			}
 		}
+		if (shortest.length() <= 0) return null;
 		return shortest;
 	}
 
-	public static Range shortestSupersequence(int[] big, int[] small) {
-		int[] closures = getClosures(big, small);
-		return getShortestClosure(closures);
-	}
-	
 	public static void main(String[] args) {
-		int[] array = {7, 5, 9, 0, 2, 1, 3, 5, 7, 9, 1, 1, 5, 8, 9, 7};
+		int[] array = {9, 2, 4, 6, 2, 5, 9};
 		int[] set = {1, 5, 9};
 		System.out.println(array.length);
 		Range shortest = shortestSupersequence(array, set);
-		System.out.println(shortest.getStart() + ", " + shortest.getEnd());
+		if (shortest == null) {
+			System.out.println("No valid subsequence.");
+		} else {
+			System.out.println(shortest.getStart() + ", " + shortest.getEnd());
+		}
 
 	}
 

Java/Ch 17. Hard/Q17_18_Shortest_Supersequence/QuestionD.java

@@ -17,7 +17,11 @@ public static Range getShortestClosure(ArrayList<Queue<Integer>> lists) {
 
 		/* Insert min element from each list. */ 
 		for (int i = 0; i < lists.size(); i++) {
-			int head = lists.get(i).remove();
+			Queue<Integer> list = lists.get(i);
+			if (list == null || list.size() == 0) {
+				return null;
+			}
+			int head = list.remove();
 			minHeap.add(new HeapNode(head, i));
 			max = Math.max(max, head);
 		}

Java/Ch 17. Hard/Q17_18_Shortest_Supersequence/QuestionE.java

@@ -0,0 +1,94 @@
+package Q17_18_Shortest_Supersequence;
+
+import java.util.HashMap;
+
+public class QuestionE {
+	/* CountedLookup acts a simple hash table with increment/decrement functions
+	 * which can efficiently tell you how many values in the hash table are
+	 * at least one. 
+	 */
+	public static class CountedLookup {
+		HashMap<Integer, Integer> lookup = new HashMap<Integer, Integer>();
+		int fulfilled = 0;
+		public CountedLookup(int[] array) {
+			for (int a : array) {
+				lookup.put(a, 0);
+			}
+		}
+		
+		public boolean contains(int v) {
+			return lookup.containsKey(v);
+		}
+		
+		public void incrementIfFound(int v) {
+			if (!contains(v)) return;
+			if (lookup.getOrDefault(v, 0) == 0) {
+				fulfilled += 1;
+			}			
+			lookup.put(v, lookup.getOrDefault(v, 0) + 1);
+		}
+		
+		public void decrementIfFound(int v) {
+			if (!contains(v)) return;
+			lookup.put(v, lookup.getOrDefault(v, 0) - 1);
+			if (lookup.getOrDefault(v, 0) == 0) {
+				fulfilled -= 1;
+			}
+		}		
+		
+		public boolean areAllFulfilled() {
+			return fulfilled == lookup.keySet().size();
+		}
+	}
+	
+	/* Find shortest subarray which contains all elements from small. */
+	public static Range shortestSupersequence(int[] big, int[] small) {
+		if (big.length < small.length) return null;
+		
+		CountedLookup countedLookup = new CountedLookup(small);
+		Range best = null;
+		int right = 0;
+		countedLookup.incrementIfFound(big[0]); // Take in left
+		for (int left = 0; left < big.length; left++) {
+			right = findClosure(big, right, countedLookup); // Move right to closure end
+			if (!countedLookup.areAllFulfilled()) { // No closure -> break
+				break;
+			}
+			
+			/* Update biggest range. */
+			int length = right - left + 1;
+			if (best == null || best.length() > length) {
+				best = new Range(left, right);
+			}
+			countedLookup.decrementIfFound(big[left]); // Drop leftmost element
+		}
+		return best;
+	}
+	
+	/* Find closure for index, and update countedlookup */
+	public static int findClosure(int[] big, int startIndex, CountedLookup countedLookup) {
+		int index = startIndex;
+		
+		/* Move forward until everything is fulfilled. */
+		while (!countedLookup.areAllFulfilled() && index + 1 < big.length) {
+			index++;
+			countedLookup.incrementIfFound(big[index]);
+		}
+		return index;	
+	}	
+	
+	public static void main(String[] args) {
+		int[] array = {7, 5, 9, 0, 2, 1, 3, 5, 7, 9, 1, 1, 5, 8, 8, 9, 7};
+		int[] set = {1, 5, 9};
+		Range shortest = shortestSupersequence(array, set);
+		if (shortest == null) {
+			System.out.println("not found");
+		} else {
+			System.out.println(shortest.toString());
+			for (int i = shortest.getStart(); i <= shortest.getEnd(); i++) {
+				System.out.print(array[i] + ", ");
+			}
+		}
+	}
+
+}

Java/Ch 17. Hard/Q17_18_Shortest_Supersequence/Range.java

@@ -12,6 +12,36 @@ public int length() {
 		return end - start + 1;
 	}
 
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		result = prime * result + end;
+		result = prime * result + start;
+		return result;
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		Range other = (Range) obj;
+		if (end != other.end)
+			return false;
+		if (start != other.start)
+			return false;
+		return true;
+	}
+
+	@Override
+	public String toString() {
+		return "Range [start=" + start + ", end=" + end + "]";
+	}
+
 	public boolean shorterThan(Range other) {
 		return length() < other.length();
 	}

Java/Ch 17. Hard/Q17_18_Shortest_Supersequence/Tester.java

@@ -1,26 +1,47 @@
 package Q17_18_Shortest_Supersequence;
 
-public class Tester {
+import CtCILibrary.AssortedMethods;
 
-	/**
-	 * @param args
-	 */
-	public static void main(String[] args) {
-		int[] array = {9, 5, 1, 0, 2, 1, 3, 5, 7, 9, 1, 1, 5, 8, 9, 7};
-		int[] set = {1, 5, 9};
-		
-		Range shortestA = QuestionA.shortestSupersequence(array, set);
-		Range shortestB = QuestionB.shortestSupersequence(array, set);
-		Range shortestC = QuestionC.shortestSupersequence(array, set);
-		Range shortestD = QuestionD.shortestSupersequence(array, set);
+public class Tester {
+	public static boolean equivalent(Range[] ranges) {
+		if (ranges[0] == null) {
+			for (Range r : ranges) {
+				if (r != null) return false;
+			}
+			return true;
+		}
 
+		int targetLength = ranges[0].length();
+		for (Range r : ranges) {
+			int length = r == null ? 0 : r.length();
+			if (targetLength != length) {
+				return false;
+			}
+		}
 
-		if (shortestA.length() != shortestB.length() || 
-			shortestB.length() != shortestC.length() || 
-			shortestC.length() != shortestD.length()) {
-			System.out.println("Mismatching.");
-		} else {
-			System.out.println("Matching: " + shortestA.length());
+		return true;
+	}
+	
+	
+	public static void main(String[] args) {
+		for (int i = 0; i < 100; i++) {
+			int[] array = AssortedMethods.randomArray(i,  0,  15);
+			int[] set = {0, 5, 8, 10};
+			
+			Range[] ranges = new Range[5];
+			
+			ranges[0] = QuestionA.shortestSupersequence(array, set);
+			ranges[1] = QuestionB.shortestSupersequence(array, set);
+			ranges[2] = QuestionC.shortestSupersequence(array, set);
+			ranges[3] = QuestionD.shortestSupersequence(array, set);
+			ranges[4] = QuestionE.shortestSupersequence(array, set);
+			
+			if (!equivalent(ranges)) {
+				System.out.println("Mismatching.");
+			} else {
+				int length = ranges[0] == null ? 0 : ranges[0].length();
+				System.out.println("Matching: " + length);
+			}
 		}
 	}