Merge Intervals

Author: TonyKim9401

merge-intervals/TonyKim9401.java

@@ -0,0 +1,30 @@
+// TC: O(n log n)
+// It takes n log n to sort array, visit all elements in O(n) time, total O(n log n)
+// SC: O(n)
+// Needs max O(n) space to save intervals
+class Solution {
+    public int[][] merge(int[][] intervals) {
+        int n = intervals.length;
+        if (n == 1) return intervals;
+
+        Arrays.sort(intervals, (a, b) -> Integer.compare(a[0], b[0]));
+        List<int[]> output = new ArrayList<>();
+        output.add(intervals[0]);
+
+        int[] currentInterval = intervals[0];
+
+        for (int[] interval : intervals) {
+            int currentEnd = currentInterval[1];
+            int nextStart = interval[0];
+            int nextEnd = interval[1];
+            if (currentEnd >= nextStart) {
+                currentInterval[1] = Math.max(currentEnd, nextEnd);
+            } else {
+                currentInterval = interval;
+                output.add(currentInterval);
+            }
+        }
+
+        return output.toArray(new int[output.size()][]);
+    }
+}