README + 56

Author: Cappuccinuo

Array/56. Merge Intervals/README.md

@@ -0,0 +1,30 @@
+Time spent : 10 min (Self + see hint)
+
+GIVEN: a collection of intervals
+
+RETURNS: the merged array that merge all overlapping intervals
+
+EXAMPLES:
+
+Input: 
+
+```
+[1,3],[2,6],[8,10],[15,18]
+```
+
+Output:[1,6],[8,10],[15,18]
+
+
+
+Use sort to first sort all the intervals.
+
+    private class IntervalComparator implements Comparator<Interval> {
+        @Override
+        public int compare(Interval i1, Interval i2) {
+            return i1.start < i2.start ? -1 : i1.start == i2.start ? 0 : 1;
+        }
+    }
+Go through the intervals. If last one's end is smaller than current interval's start, then add current interval.
+
+Otherwise change last interval's end to the max of last interval's end or current interval's end.
+

Array/56. Merge Intervals/Solution.java

@@ -0,0 +1,32 @@
+/**
+ * Definition for an interval.
+ * public class Interval {
+ *     int start;
+ *     int end;
+ *     Interval() { start = 0; end = 0; }
+ *     Interval(int s, int e) { start = s; end = e; }
+ * }
+ */
+class Solution {
+    public List<Interval> merge(List<Interval> intervals) {
+        Collections.sort(intervals, new IntervalComparator());
+        LinkedList<Interval> merged = new LinkedList<>();
+        
+        for (Interval interval : intervals) {
+            if (merged.size() == 0 || merged.getLast().end < interval.start) {
+                merged.add(interval);
+            }
+            else {
+                merged.getLast().end = Math.max(merged.getLast().end, interval.end);
+            }
+        }
+        return merged;
+    }
+    
+    private class IntervalComparator implements Comparator<Interval> {
+        @Override
+        public int compare(Interval i1, Interval i2) {
+            return i1.start < i2.start ? -1 : i1.start == i2.start ? 0 : 1;
+        }
+    }
+}

README.md

@@ -257,6 +257,7 @@
 | 253  | 229  |        [Majority Element II][229]        |     Java     |   Medium   |       2018.1.6        |                  Array                   |                       |
 | 254  | 570  | [Managers with at Least 5 Direct Reports][570] |     SQL      |   Medium   |       2018.1.6        |                 DataBase                 |                       |
 | 255  | 596  |   [Classes More Than 5 Students][596]    |     SQL      |    Easy    |       2018.1.6        |                 DataBase                 |                       |
+| 256  |  56  |          [Merge Intervals][56]           |     Java     |   Medium   |       2018.1.6        |                  Array                   |                       |
 
 
 [1]:<https://leetcode.com/problems/two-sum/> "Two Sum"
@@ -289,6 +290,7 @@
 [51]:<https://leetcode.com/problems/n-queens/> "N-Queens"
 [52]:<https://leetcode.com/problems/n-queens-ii/> "N-Queens II"
 [53]:<https://leetcode.com/problems/maximum-subarray/> "Maximum Subarray"
+[56]:<https://leetcode.com/problems/merge-intervals/> "Merge Intervals"
 [58]:<https://leetcode.com/problems/length-of-last-word/> "Length of Last Word"
 [61]:<https://leetcode.com/problems/rotate-list/> "Rotate List"
 [62]:<https://leetcode.com/problems/unique-paths/> "Unique Paths"