Create Write Priority Queue Using Heap.java

Java/Write Priority Queue Using Heap.java

@@ -0,0 +1,116 @@
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+  public static class PriorityQueue {
+    ArrayList<Integer> data;
+
+    public PriorityQueue() {
+      data = new ArrayList<>();
+    }
+
+    public void add(int val) {
+      // write your code here
+      data.add(val);
+      upheapify(data.size()-1);
+
+    }
+
+    private void upheapify(int i){
+        if(i==0){
+            return;
+        }
+        int pi = (i-1)/2;
+        if(data.get(i) < data.get(pi)){
+            swap(i,pi);
+            upheapify(pi);
+        }
+
+    }
+    private void swap(int i,int j){
+        int ith = data.get(i);
+        int jth = data.get(j);
+        data.set(i,jth);
+        data.set(j,ith);
+    }
+
+    public int remove() {
+      // write your code here
+      if(this.size()==0){
+          System.out.println("Underflow");
+          return -1;
+      }
+      swap(0,data.size() -1);
+
+      int val =   data.remove(data.size()-1);
+      downheapify(0);
+
+      return val;
+
+
+
+    }
+
+    private void downheapify(int pi){
+        int min = pi;
+        int lc = 2*pi+1;
+        if(lc < data.size() && data.get(lc) < data.get(min)){
+            min = lc;
+        }
+        int rc = 2*pi + 2;
+        if(rc < data.size() && data.get(rc) < data.get(min)){
+            min = rc;
+        }
+
+        if(min != pi){
+            swap(pi,min);
+            downheapify(min);
+        }
+
+    }
+
+    public int peek() {
+      // write your code here
+
+      if(this.size()==0){
+          System.out.println("Underflow");
+          return -1;
+      }else{
+          return data.get(0);
+      }
+
+    }
+
+    public int size() {
+      // write your code here
+      return data.size();
+    }
+  }
+
+  public static void main(String[] args) throws Exception {
+    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    PriorityQueue qu = new PriorityQueue();
+
+    String str = br.readLine();
+    while (str.equals("quit") == false) {
+      if (str.startsWith("add")) {
+        int val = Integer.parseInt(str.split(" ")[1]);
+        qu.add(val);
+      } else if (str.startsWith("remove")) {
+        int val = qu.remove();
+        if (val != -1) {
+          System.out.println(val);
+        }
+      } else if (str.startsWith("peek")) {
+        int val = qu.peek();
+        if (val != -1) {
+          System.out.println(val);
+        }
+      } else if (str.startsWith("size")) {
+        System.out.println(qu.size());
+      }
+      str = br.readLine();
+    }
+  }
+}