Day22q3

Day 22/aishwarya--J.md

@@ -0,0 +1,18 @@
+```
+class Solution {
+    public int minOperations(int[] nums) {
+        var counter = new HashMap<Integer, Integer>();
+        for (int num: nums) {
+            counter.put(num, counter.getOrDefault(num, 0) + 1);
+        }
+        int ans = 0;
+        for (int c: counter.values()) {
+            if (c == 1) {
+                return -1;
+            }
+            ans += Math.ceil((double) c / 3);
+        }
+        return ans;
+    }
+}
+```

Day 22/q1.md

@@ -0,0 +1,29 @@
+You are given a 0-indexed array nums consisting of positive integers.
+
+There are two types of operations that you can apply on the array any number of times:
+
+Choose two elements with equal values and delete them from the array.
+Choose three elements with equal values and delete them from the array.
+Return the minimum number of operations required to make the array empty, or -1 if it is not possible.
+
+Example 1:
+
+Input: nums = [2,3,3,2,2,4,2,3,4]
+Output: 4
+Explanation: We can apply the following operations to make the array empty:
+
+Apply the first operation on the elements at indices 0 and 3. The resulting array is nums = [3,3,2,4,2,3,4].
+Apply the first operation on the elements at indices 2 and 4. The resulting array is nums = [3,3,4,3,4].
+Apply the second operation on the elements at indices 0, 1, and 3. The resulting array is nums = [4,4].
+Apply the first operation on the elements at indices 0 and 1. The resulting array is nums = [].
+It can be shown that we cannot make the array empty in less than 4 operations.
+Example 2:
+
+Input: nums = [2,1,2,2,3,3]
+Output: -1
+Explanation: It is impossible to empty the array.
+
+Constraints:
+
+2 <= nums.length <= 105
+1 <= nums[i] <= 106

Day 22/q3.md

@@ -0,0 +1,14 @@
+## sort list
+Given the head of a linked list, return the list after sorting it in ascending order.
+
+Example 1:
+Input: head = [4,2,1,3]
+Output: [1,2,3,4]
+
+Example 2:
+Input: head = [-1,5,3,4,0]
+Output: [-1,0,3,4,5]
+
+Example 3:
+Input: head = []
+Output: []

Day 22/q3_aishwarya--J.md

@@ -0,0 +1,51 @@
+```
+public class Solution {
+
+  public ListNode sortList(ListNode head) {
+    if (head == null || head.next == null)
+      return head;
+
+    // step 1. cut the list to two halves
+    ListNode prev = null, slow = head, fast = head;
+
+    while (fast != null && fast.next != null) {
+      prev = slow;
+      slow = slow.next;
+      fast = fast.next.next;
+    }
+
+    prev.next = null;
+
+    // step 2. sort each half
+    ListNode l1 = sortList(head);
+    ListNode l2 = sortList(slow);
+
+    // step 3. merge l1 and l2
+    return merge(l1, l2);
+  }
+
+  ListNode merge(ListNode l1, ListNode l2) {
+    ListNode l = new ListNode(0), p = l;
+
+    while (l1 != null && l2 != null) {
+      if (l1.val < l2.val) {
+        p.next = l1;
+        l1 = l1.next;
+      } else {
+        p.next = l2;
+        l2 = l2.next;
+      }
+      p = p.next;
+    }
+
+    if (l1 != null)
+      p.next = l1;
+
+    if (l2 != null)
+      p.next = l2;
+
+    return l.next;
+  }
+
+}
+```