Add the solution for leetcode problem #56

Author: rayworks

src/main/java/org/sean/array/IntervalMerger.java

@@ -0,0 +1,65 @@
+package org.sean.array;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+/***
+ * 56. Merge Intervals
+ */
+public class IntervalMerger {
+    public int[][] merge(int[][] intervals) {
+        if (intervals.length <= 1) return intervals;
+
+        int i = 0, j = 1;
+        int len = intervals.length;
+
+        // sort by the start point N*lgN
+        Arrays.sort(intervals, Comparator.comparingInt(o -> o[0]));
+
+        int reducedCnt = 0;
+        while (i < j && j < len) {
+            int[] merged = doMerge(intervals[i], intervals[j]);
+            if (merged == null) {
+                i = j;
+                j++;
+            } else {
+                intervals[i][0] = merged[0];
+                intervals[i][1] = merged[1];
+
+                // marked as merged
+                intervals[j][0] = -1;
+                intervals[j][1] = -1;
+
+                ++reducedCnt;
+
+                j++;
+            }
+        }
+
+        return filterMergedArray(intervals, reducedCnt, len);
+    }
+
+    int[] doMerge(int[] line1, int[] line2) {
+        int s1 = line1[0];
+        int e1 = line1[1];
+        int s2 = line2[0];
+        int e2 = line2[1];
+
+        if (s2 > e1) {
+            return null;
+        } else {
+            return new int[]{s1, Math.max(e1, e2)};
+        }
+    }
+
+    private int[][] filterMergedArray(int[][] intervals, int reducedCnt, int len) {
+        int[][] out = new int[len - reducedCnt][2];
+        int m = 0;
+        for (int k = 0; k < len; k++) {
+            if (intervals[k][0] >= 0) {
+                out[m++] = intervals[k];
+            }
+        }
+        return out;
+    }
+}

src/test/java/org/sean/array/IntervalMergerTest.java

@@ -0,0 +1,27 @@
+package org.sean.array;
+
+import junit.framework.TestCase;
+
+import static org.junit.Assert.assertArrayEquals;
+
+public class IntervalMergerTest extends TestCase {
+
+    private IntervalMerger merger;
+
+    public void setUp() throws Exception {
+        merger = new IntervalMerger();
+    }
+
+    public void testMerge() {
+        int[][] intervals = {{2, 3}, {4, 5}, {6, 7}, {8, 9}, {1, 10}};
+        assertArrayEquals(new int[][]{{1, 10}}, merger.merge(intervals));
+
+        intervals = new int[][]{{1, 4}, {4, 5}};
+        assertArrayEquals(new int[][]{{1, 5}}, merger.merge(intervals));
+
+        intervals = new int[][]{
+                {3, 3}, {1, 1}, {0, 2}, {2, 2}, {1, 2}, {1, 3}, {1, 1}, {3, 3}, {2, 3}, {4, 6}
+        };
+        assertArrayEquals(new int[][]{{0, 3}, {4, 6}}, merger.merge(intervals));
+    }
+}