sorting: HeapSort

OneCodeMonkey · OneCodeMonkey · commit 946fad62496d · 2019-08-17T20:17:53.000+08:00
diff --git a/Algorithm_full_features/sort/HeapSort.java b/Algorithm_full_features/sort/HeapSort.java
@@ -0,0 +1,60 @@
+/**
+ * sorts a sequence of strings from standard input using heapsort.
+ * The `HeapSort` class provides a static methods for heapsorting an array.
+ *
+ */
+public class HeapSort{
+	private HeapSort() {}
+
+	// rearranges the array in ascending order, using the natural order.
+	public static void sort(Comparable[] pq) {
+		int n = pq.length;
+		for(int k = n / 2; k >= 1; k--) {
+			sink(pq, k, n);
+		}
+
+		while(n > 1){
+			exchange(pa, 1, n--);
+			sink(pq, 1, n);
+		}
+	}
+
+	// Helper functions
+	private static void sink(Comparable[] pq, int k, int n) {
+		while(2 * k <= n) {
+			int j = 2 * k;
+			if(j < n && less(pq, j, j + 1))
+				j++;
+			if(!less(pq, k, j))
+				break;
+			exchange(pq, k, j);
+			k = j;
+		}
+	}
+
+	// helper functions for comparisons and swaps
+	// indices are "off-by-one" to support 1-based indexing.
+	private static boolean less(Comparable[] pq, int i, int j) {
+		return pq[i - 1].compareTo(pq[j - 1]) < 0;
+	}
+
+	private static void exchange(Object[] pq, int i, int j) {
+		Object swap = pq[i - 1];
+		pq[i - 1] = pq[j - 1];
+		pq[j - 1] = swap;
+	}
+
+	// print
+	private static void show(Comparable[] a) {
+		for(int i = 0; i < a.length; i++) {
+			StdOut.println(a[i]);
+		}
+	}
+
+	// test
+	public static void main(String[] args) {
+		String[] a = StdIn.readAllStrings();
+		Heap.sort(a);
+		show(a);
+	}
+}
