merges two sorted halves of an array into a single sorted array. - Java Collection Framework

Java examples for Collection Framework:Array Sort

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Description

merges two sorted halves of an array into a single sorted array.

Demo Code


//package com.java2s;
import java.util.ArrayList;

public class Main {
    /**//  w  ww.  j ava2 s  .c o m
     * merges two sorted halves of an array into a single sorted array. Assumes that the input array to be sorted 
     *    has fully sorted sub-arrays to the left and right of some particular index
     * 
     * @param arrayList the ArrayList whose sub-arrays you want to merge
     * @param tempArray a working array that will hold the merged array as it is being built from the sub-arrays of ArrayList
     * @param first the starting index of left side's sorted sub-array
     * @param mid the starting index of the right side's sorted sub-array
     * @param last the ending index of the right side's sorted sub-array
     */
    public static <T extends Comparable<? super T>> void merge(
            ArrayList<T> arrayList, T[] tempArray, int first, int mid,
            int last) {
        if (last > first && last >= mid && mid >= first) {
            int tempIndex = first;
            int start1 = first;
            int end1 = mid - 1;
            int start2 = mid;
            int end2 = last;
            while ((end1 - start1) > -1 && (end2 - start2) > -1) {
                if (arrayList.get(start1).compareTo(arrayList.get(start2)) <= 0) {
                    tempArray[tempIndex] = arrayList.get(start1);
                    start1++;
                } else {
                    tempArray[tempIndex] = arrayList.get(start2);
                    start2++;
                }
                tempIndex++;
            }
            // assume that one of the sub-arrays has been completely been added to the temporary array by this point
            while ((end1 - start1) > -1) {
                tempArray[tempIndex] = arrayList.get(start1);
                start1++;
                tempIndex++;
            }
            while ((end2 - start2) > -1) {
                tempArray[tempIndex] = arrayList.get(start2);
                start2++;
                tempIndex++;
            }
            for (int i = first; i <= last; i++) {
                arrayList.set(i, tempArray[i]);
            }
        }
    }
}

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