finish "56. Merge Intervals". Fix #56

Author: diguage

README.adoc

@@ -284,11 +284,11 @@
 |{source_base_url}/JumpGame.java[Java]
 |Medium
 
-//|56
-//|{leetcode_base_url}/merge-intervals/[Merge Intervals]
-//|{source_base_url}/MergeIntervals.java[Java]
-//|Medium
-//
+|56
+|{leetcode_base_url}/merge-intervals/[Merge Intervals]
+|{source_base_url}/MergeIntervals.java[Java]
+|Medium
+
 //|57
 //|{leetcode_base_url}/insert-interval/[Insert Interval]
 //|{source_base_url}/InsertInterval.java[Java]

src/main/java/com/diguage/algorithm/leetcode/MergeIntervals.java

@@ -0,0 +1,72 @@
+package com.diguage.algorithm.leetcode;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.Objects;
+
+import static com.diguage.algorithm.util.PrintUtils.printMatrix;
+
+/**
+ * = 56. Merge Intervals
+ *
+ * https://leetcode.com/problems/merge-intervals/[Merge Intervals - LeetCode]
+ *
+ * Given a collection of intervals, merge all overlapping intervals.
+ *
+ * .Example 1:
+ * [source]
+ * ----
+ * Input: [[1,3],[2,6],[8,10],[15,18]]
+ * Output: [[1,6],[8,10],[15,18]]
+ * Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].
+ * ----
+ *
+ * .Example 2:
+ * [source]
+ * ----
+ * Input: [[1,4],[4,5]]
+ * Output: [[1,5]]
+ * Explanation: Intervals [1,4] and [4,5] are considered overlapping.
+ * ----
+ *
+ * *NOTE:* input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.
+ *
+ * @author D瓜哥, https://www.diguage.com/
+ * @since 2019-10-23 12:27
+ */
+public class MergeIntervals {
+    public int[][] merge(int[][] intervals) {
+        if (Objects.isNull(intervals) || intervals.length <= 1) {
+            return intervals;
+        }
+        Arrays.sort(intervals, Comparator.comparingInt(o -> o[0]));
+        int index = 0;
+        for (int i = 1; i < intervals.length; i++) {
+            if (index < 0 || intervals[index][1] < intervals[i][0]) {
+                intervals[index + 1] = intervals[i];
+                index++;
+            } else {
+                intervals[index][1] = Math.max(intervals[i][1], intervals[index][1]);
+            }
+        }
+        return Arrays.copyOf(intervals, index + 1);
+    }
+
+    public static void main(String[] args) {
+        MergeIntervals solution = new MergeIntervals();
+        int[][] matrix = {{8, 10}, {2, 6}, {15, 18}, {1, 3}};
+        printMatrix(matrix);
+        int[][] r1 = solution.merge(matrix);
+        printMatrix(r1);
+
+        int[][] matrix2 = {{1, 4}, {4, 5}};
+        printMatrix(matrix2);
+        int[][] r2 = solution.merge(matrix2);
+        printMatrix(r2);
+
+        int[][] matrix3 = {{1, 9}, {2, 5}, {19, 20}, {10, 11}, {12, 20}, {0, 3}, {0, 1}, {0, 2}};
+        printMatrix(matrix3);
+        int[][] r3 = solution.merge(matrix3);
+        printMatrix(r3);
+    }
+}