heap done

heap/KLargestElementStream.java

@@ -0,0 +1,60 @@
+package heap;
+
+import java.util.PriorityQueue;
+import java.util.Scanner;
+
+public class KLargestElementStream {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+
+        int n = sc.nextInt();
+
+        if (n <= 0) {
+            System.out.println("The size of array should be greater than 0.");
+            sc.close();
+            return;
+        }
+
+        int k = sc.nextInt();
+        if (k < 1 || k > n) {
+            System.out.println("The value of k should be in range of 1 and " + n + '.');
+            sc.close();
+            return;
+        }
+
+        int[] arr = new int[n];
+
+        for (int i = 0; i < n; i++) {
+            arr[i] = sc.nextInt();
+        }
+
+        System.out.println(kthLargest(arr, n, k));
+
+        sc.close();
+    }
+
+    static int[] kthLargest(int[] arr, int n, int k) {
+        int[] res = new int[n];
+
+        PriorityQueue<Integer> pq = new PriorityQueue<>();
+
+        for (int i = 0; i < n; i++) {
+            if (pq.size() < k) {
+                pq.offer(arr[i]);
+            } else {
+                if (arr[i] > pq.peek()) {
+                    pq.poll();
+                    pq.offer(arr[i]);
+                }
+            }
+
+            if (pq.size() >= k) {
+                res[i] = pq.peek();
+            } else {
+                res[i] = -1;
+            }
+        }
+
+        return res;
+    }
+}

heap/RearrangeCharacters.java

@@ -0,0 +1,60 @@
+package heap;
+
+import java.util.PriorityQueue;
+import java.util.Scanner;
+
+public class RearrangeCharacters {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+
+        String str = sc.nextLine();
+
+        System.out.println(rearrangeCharacters(str));
+
+        sc.close();
+    }
+
+    static String rearrangeCharacters(String s) {
+        int[] map = new int[26];
+        for (char ch : s.toCharArray()) {
+            map[ch - 'a']++;
+        }
+
+        StringBuilder ans = new StringBuilder();
+        PriorityQueue<Pair> pq = new PriorityQueue<>((a, b) -> b.freq - a.freq);
+
+        for (int i = 0; i < 26; i++) {
+            if (map[i] > 0) {
+                pq.offer(new Pair((char) ('a' + i), map[i]));
+            }
+        }
+
+        Pair hold = pq.poll();
+        ans.append(hold.ch);
+        hold.freq--;
+
+        while (!pq.isEmpty()) {
+            Pair curr = pq.poll();
+            ans.append(curr.ch);
+            curr.freq--;
+
+            if (hold.freq > 0) {
+                pq.offer(hold);
+            }
+
+            hold = curr;
+        }
+
+        return ans.length() == s.length() ? ans.toString() : "";
+    }
+}
+
+class Pair {
+    char ch;
+    int freq;
+
+    public Pair(char ch, int freq) {
+        this.ch = ch;
+        this.freq = freq;
+    }
+}