Merge pull request neetcode-gh#367 from bubbleship/main

Update 347-Top-K-Frequent-Elements.java

java/347-Top-K-Frequent-Elements.java

@@ -1,4 +1,8 @@
-class Solution {
+class Solution1 {
+ /**
+ * Time Complexity: O(nlog(k))
+ * Space Complexity: O(n)
+ */
  public int[] topKFrequent(int[] nums, int k) {
  int[] arr = new int[k];
  HashMap<Integer, Integer> map = new HashMap<>();
@@ -17,3 +21,57 @@ public int[] topKFrequent(int[] nums, int k) {
  return arr;
  }
 }
+
+class Solution2 {
+ /**
+ * Time Complexity: O(n)
+ * Space Complexity: O(n)
+ */
+ public int[] topKFrequent(int[] numbers, int k) {
+ HashMap<Integer, Integer> map = new HashMap<>();
+ for (int number : numbers)
+ map.put(number, map.getOrDefault(number, 0) + 1);
+
+ int size = map.size();
+ int[] keys = new int[size];
+ int i = 0;
+ for (int key : map.keySet())
+ keys[i++] = key;
+
+ select(keys, map, 0, size - 1, size - k);
+ return Arrays.copyOfRange(keys, size - k, size);
+ }
+
+ // Modified implementation of Hoare's selection algorithm:
+
+ private void select(int[] keys, Map<Integer, Integer> map, int left, int right, int kSmallest) {
+ while (left != right) {
+ int pivot = partition(keys, map, left, right, (left + right) / 2);
+
+ if (kSmallest == pivot) return;
+
+ if (kSmallest < pivot) right = pivot - 1;
+ else left = pivot + 1;
+ }
+ }
+
+ private int partition(int[] keys, Map<Integer, Integer> map,int left, int right, int pivot) {
+ int pivotValue = map.get(keys[pivot]);
+ swap(keys, pivot, right);
+ int index = left;
+
+ for (int i = left; i <= right; i++)
+ if (map.get(keys[i]) < pivotValue) {
+ swap(keys, i, index);
+ index++;
+ }
+ swap(keys, right, index);
+ return index;
+ }
+
+ private void swap(int[] array, int i1, int i2) {
+ int temp = array[i1];
+ array[i1] = array[i2];
+ array[i2] = temp;
+ }
+}