forked from Hithomelabs/Princeton1
74 lines
2.2 KiB
Java
74 lines
2.2 KiB
Java
package com.hithomelabs.princeton1.module6;
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import com.hithomelabs.princeton1.module5.ComparableSort;
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import com.hithomelabs.princeton1.module5.MeasurableSort;
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import com.hithomelabs.princeton1.module5.SortingMetaData;
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import java.util.Arrays;
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import java.util.Comparator;
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public class Merge<E> implements MeasurableSort<E> {
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@Override
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public void sort(E[] arr) {
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coreSortLogic(arr, null, null);
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}
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private void coreSortLogic(E[] arr, Comparator<E> cmp, SortingMetaData metaData) {
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int N = arr.length;
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// * * aux is a helper array required for merge
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E[] aux = Arrays.copyOf(arr, N);
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mergesort(arr, aux, 0, N - 1, cmp, metaData);
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}
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private void mergesort(E[] arr, E[] aux, int lo, int hi, Comparator<E> cmp, SortingMetaData metaData) {
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if (hi <= lo) return;
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int mid = lo + (hi - lo) / 2;
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mergesort(arr, aux, lo, mid, cmp, metaData);
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mergesort(arr, aux, mid + 1, hi, cmp, metaData);
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merge(arr, aux, lo, mid, hi, cmp, metaData);
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}
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private void merge(E[] arr, E[] aux, int lo, int mid, int hi, Comparator<E> cmp, SortingMetaData metaData) {
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// * * creating backup of original array
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for (int i = lo; i <= hi; i++)
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aux[i] = arr[i];
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int i = lo;
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int j = mid + 1;
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for (int k = lo; k <= hi; k++) {
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// * If i has already reached mid, no need to compare we insert at pointer k
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if (i > mid) {
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arr[k] = aux[j++];
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if (metaData != null)
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metaData.incrementCompares();
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} else if (j > hi) {
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arr[k] = aux[i++];
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if (metaData != null)
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metaData.incrementCompares();
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} else if (less( aux[i], aux[j], cmp, metaData)) {
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arr[k] = aux[i++];
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}
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else arr[k] = aux[j++];
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}
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}
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@Override
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public void sort(E[] arr, Comparator<E> cmp, SortingMetaData metaData) {
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if (metaData != null)
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metaData.startTime();
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coreSortLogic(arr, cmp, metaData);
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if (metaData != null)
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metaData.endTime();
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}
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@Override
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public void sort(E[] arr, Comparator<E> cmp) {
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coreSortLogic(arr, cmp, null);
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}
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}
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