Java Chapter 9: Intervals

java/Intervals/IdentifyAllIntervalOverlaps.java

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+import java.util.ArrayList;
+import java.util.List;
+
+import DS.Interval;
+
+/*
+    // Definition of Interval:
+    class Interval {
+        public int start;
+        public int end;
+        public Interval(int start, int end) {
+            this.start = start;
+            this.end = end;
+        }
+    }
+ */
+
+public class IdentifyAllIntervalOverlaps {
+    public List<Interval> identifyAllIntervalOverlaps(List<Interval> intervals1, List<Interval> intervals2) {
+        List<Interval> overlaps = new ArrayList<>();
+        int i, j;
+        i = j = 0;
+        while (i < intervals1.size() && j < intervals2.size()) {
+            // Set A to the interval that starts first and B to the other 
+            // interval.
+            Interval A, B;
+            if (intervals1.get(i).start <= intervals2.get(j).start) {
+                A = intervals1.get(i);
+                B = intervals2.get(j);
+            } else {
+                A = intervals2.get(j);
+                B = intervals1.get(i);
+            }
+            // If there's an overlap, add the overlap.
+            if (A.end >= B.start) {
+                overlaps.add(new Interval(B.start, Math.min(A.end, B.end)));
+            }
+            // Advance the pointer associated with the interval that ends 
+            // first.
+            if (intervals1.get(i).end < intervals2.get(j).end) {
+                i++;
+            } else {
+                j++;
+            }
+        }
+        return overlaps;
+    }
+}

java/Intervals/LargestOverlapOfIntervals.java

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+import java.util.ArrayList;
+import java.util.List;
+
+import DS.Interval;
+
+/*
+    // Definition of Interval:
+    class Interval {
+        public int start;
+        public int end;
+        public Interval(int start, int end) {
+            this.start = start;
+            this.end = end;
+        }
+    }
+ */
+
+public class LargestOverlapOfIntervals {
+    public int largestOverlapOfIntervals(List<Interval> intervals) {
+        List<int[]> points = new ArrayList<>();
+        for (Interval interval : intervals) {
+            points.add(new int[]{interval.start, 'S'});
+            points.add(new int[]{interval.end, 'E'});
+        }
+        // Sort in chronological order. If multiple points occur at the same 
+        // time, ensure end points are prioritized before start points.
+        Collections.sort(points, (a, b) -> {
+            if (a[0] == b[0]) return Integer.compare(a[1], b[1]);
+            else return Integer.compare(a[0], b[0]);
+        });
+        int activeInterval= 0;
+        int maxOverlaps = 0;
+        for (int[] point : points) {
+            int time = point[0];
+            int pointType = point[1];
+            if (pointType == 'S') {
+                activeInterval++;
+            } else {
+                activeInterval--;
+            }
+            maxOverlaps = Math.max(maxOverlaps, activeInterval);
+        }
+        return maxOverlaps;
+    }
+}

java/Intervals/MergeOverlappingIntervals.java

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+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import DS.Interval;
+
+/*
+    // Definition of Interval:
+    class Interval {
+        public int start;
+        public int end;
+        public Interval(int start, int end) {
+            this.start = start;
+            this.end = end;
+        }
+    }
+ */
+
+public class MergeOverlappingIntervals {
+    public List<Interval> mergeOverlappingIntervals(List<Interval> intervals) {
+        Collections.sort(intervals, (a, b) -> Integer.compare(a.start, b.start));
+        List<Interval> merged = new ArrayList<>();
+        merged.add(intervals.get(0));
+        for (int i = 1; i < intervals.size(); i++) {
+            Interval B = intervals.get(i);
+            Interval A = merged.get(merged.size() - 1);
+            // If A and B don't overlap, add B to the merged list.
+            if (A.end < B.start) {
+                merged.add(B);
+            }
+            // If they do overlap, merge A with B.
+            else {
+                A.end =  Math.max(A.end, B.end);
+            }
+        }
+        return merged;
+    }   
+}