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HeapSort.java
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60 lines (53 loc) · 1.27 KB
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/**
* 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);
}
}