190812

Author: csf0630p

406_Queue Reconstruction by Height.java

@@ -0,0 +1,17 @@
+// 1.0 greedy, O(n^2)/O(n)
+class Solution {
+    public int[][] reconstructQueue(int[][] people) {
+        if (people == null || people.length == 0 || people[0].length == 0) {
+            return new int[0][0];
+        }
+        Arrays.sort(people, (a, b) -> (a[0] == b[0] ? a[1] - b[1] : b[0] - a[0]));
+        List<int[]> res = new LinkedList<>();
+        for (int[] p : people) {
+            res.add(p[1], p);
+        }
+        return res.toArray(new int[res.size()][]);
+    }
+}
+
+// 2.0 merge sort, O(nlogn)
+// https://leetcode.com/problems/queue-reconstruction-by-height/discuss/143403/O(nlogn)-modified-merge-sort-solution-with-detailed-explanation

452_Minimum Number of Arrows to Burst Balloons.java

@@ -0,0 +1,14 @@
+//same as 435, difference : overlaps include [1,2] & [2,3], O(nlogn)/O(n)
+class Solution {
+    public int findMinArrowShots(int[][] points) {
+        if (points.length == 0) return 0;        
+        Arrays.sort(points, (a, b) -> (a[1] - b[1]));
+        int cnt = 1, end = points[0][1];
+        for (int i = 1; i < points.length; i++) {
+            if (points[i][0] <= end) continue;
+            end = points[i][1];
+            cnt++;
+        }
+        return cnt;        
+    }
+}