4kyu: add „Sum of Intervals“

Signed-off-by: Matej Focko <mfocko@redhat.com>

4kyu/sum_of_intervals/solution.java

@@ -0,0 +1,148 @@
+package cw;
+
+import java.util.TreeSet;
+
+class Interval {
+    private static class Range implements Comparable<Range> {
+        private int from;
+        private int to;
+
+        public Range(int from, int to) {
+            this.from = from;
+            this.to = to;
+        }
+
+        public int length() {
+            return to - from;
+        }
+
+        public Range merge(Range other) {
+            return new Range(Math.min(from, other.from), Math.max(to, other.to));
+        }
+
+        public boolean mergeInSitu(Range other) {
+            if (!canMerge(other)) {
+                return false;
+            }
+
+            from = Math.min(from, other.from);
+            to = Math.max(to, other.to);
+            return true;
+        }
+
+        public boolean has(int x) {
+            return from <= x && x <= to;
+        }
+
+        public boolean isSubrangeOf(Range other) {
+            return other.has(from) && other.has(to);
+        }
+
+        public boolean isPrefixOf(Range other) {
+            return from <= other.from && other.has(to);
+        }
+
+        public boolean isSuffixOf(Range other) {
+            return to >= other.to && has(other.from);
+        }
+
+        public boolean canMerge(Range other) {
+            return isSubrangeOf(other) || isPrefixOf(other) || isSuffixOf(other);
+        }
+
+        @Override
+        public int compareTo(Range other) {
+            if (other == null) {
+                throw new NullPointerException();
+            }
+
+            if (from == other.from && to == other.to) {
+                return 0;
+            }
+
+            if (to < other.from || from < other.from) {
+                return -1;
+            }
+
+            return 1;
+        }
+    }
+
+    private static void insertRange(TreeSet<Range> ranges, Range range) {
+        for (Range r : ranges) {
+            if (r.canMerge(range)) {
+                ranges.remove(r);
+                ranges.add(r.merge(range));
+                return;
+            }
+        }
+
+        ranges.add(range);
+    }
+
+    private static boolean mergeRanges(TreeSet<Range> ranges) {
+        for (Range x : ranges) {
+            for (Range y : ranges) {
+                if (x == y) {
+                    continue;
+                }
+
+                if (x.canMerge(y)) {
+                    ranges.remove(x);
+                    ranges.remove(y);
+                    ranges.add(x.merge(y));
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    public static int sumIntervals(int[][] intervals) {
+        if (intervals == null) {
+            return 0;
+        }
+
+        TreeSet<Range> ranges = new TreeSet<>();
+
+        // Go through the intervals and construct a set out of them
+        // when adding each interval, try to merge it in-situ with any of the
+        // existing intervals
+        for (int[] interval : intervals) {
+            insertRange(ranges, new Range(interval[0], interval[1]));
+        }
+
+        // then iteratively merge the set of intervals while possible
+        boolean hasChanged = true;
+        while (hasChanged) {
+            hasChanged = mergeRanges(ranges);
+        }
+
+        for (Range r : ranges) {
+            System.out.format("%d, %d; ", r.from, r.to);
+        }
+        System.out.println();
+
+        return ranges.stream().map(Range::length).reduce(Integer::sum).orElse(0);
+    }
+
+    public static void main(String[] args) {
+        // null argument
+        System.out.format("%d == %d\n", Interval.sumIntervals(null), 0);  // => 0
+
+        // empty intervals
+        System.out.format("%d == %d\n", Interval.sumIntervals(new int[][]{}), 0);  // => 0
+        System.out.format("%d == %d\n", Interval.sumIntervals(new int[][]{{2,2}, {5,5}}), 0);  // => 0
+
+        // disjoined intervals
+        System.out.format("%d == %d\n", Interval.sumIntervals(new int[][]{
+          {1,2},{3,5}
+        }), 3);  // => (2-1) + (5-3) = 3
+
+        // overlapping intervals
+        System.out.format("%d == %d\n", Interval.sumIntervals(new int[][]{
+          {1,4},{3,6},{2,8}
+        }), 7);  // [1,8] => 7
+    }
+}