stl

Author: okmd

stl/01-max-heap.cpp

@@ -0,0 +1,92 @@
+#include<iostream>
+using namespace std;
+
+class PQ {
+public:
+    int* arr;
+    int size;
+    PQ(int s) {
+        arr = new int[s];
+        size = 0;
+    }
+    int parent(int i) {
+        return (i - 1) / 2;
+    }
+    int left(int i) {
+        return 2 * i;
+    }
+    int right(int i) {
+        return 2 * i + 1;
+    }
+    void heapify_down(int i) {
+        int l = left(i);
+        int r = right(i);
+        int largest = i;
+        // change sign to convert to min-heap
+        if (l<size and arr[l]>arr[largest]) largest = l;
+        if (r<size and arr[r]>arr[largest]) largest = r;
+        if (largest != i) {
+            swap(arr[i], arr[largest]);
+            heapify_down(largest);
+        }
+    }
+    void heapify_up(int i) {
+        int p = parent(i);
+        // > for min-heap
+        if (p >= 0 and arr[p] < arr[i]) {
+            swap(arr[i], arr[p]);
+            heapify_up(p);
+        }
+    }
+    void push(int val) {
+        arr[size++] = val;
+        heapify_up(size - 1);
+    }
+    void pop() {
+        arr[0] = arr[--size];
+        heapify_down(0);
+    }
+    int top() {
+        return arr[0];
+    }
+    ~PQ() {
+        delete[]arr;
+    }
+};
+int main() {
+    PQ pq(10);
+
+    // Note: The element's value decides priority
+
+    pq.push(3);
+    pq.push(2);
+    pq.push(15);
+
+    cout << "Size is " << pq.size << endl;
+
+    cout << pq.top() << "\n ";
+    pq.pop();
+
+    cout << pq.top() << ";\n";
+    pq.pop();
+
+    pq.push(5);
+    pq.push(4);
+    pq.push(45);
+
+    cout << endl << "Size is " << pq.size << endl;
+
+    cout << pq.top() << " ";
+    pq.pop();
+
+    cout << pq.top() << " ";
+    pq.pop();
+
+    cout << pq.top() << " ";
+    pq.pop();
+
+    cout << pq.top() << " ";
+    pq.pop();
+
+    std::cout << pq.size;
+}