java实现的一个【快速排序 】算法【原创】

 

import java.util.Arrays;
import org.apache.commons.lang.ArrayUtils;

public class Test {

  public static void main(String[] args) {
    int[] sortedArrays = quickSort(new int[]{3, 5, 1, 2});
    System.out.println(ArrayUtils.toString(sortedArrays));
  }

  /**
   * Run time is O(nlogn)
   *
   * @param source source array
   * @return sorted array
   */
  private static int[] quickSort(int[] source) {

    int sourceSize = source.length;

    final byte baseLen = 2;

    // An array that is empty or contains only one element is ordered
    if (sourceSize < baseLen) {
      return source;
    }

    // pivot value
    int pivotVal = source[sourceSize / 2];

    return combineList(quickSort(sortLeft(source, pivotVal)), pivotVal, quickSort(sortRight(source, pivotVal)));
  }

  private static int[] sortLeft(int[] source, int pivotVal) {
    return sort(source, pivotVal, true);
  }

  private static int[] sortRight(int[] source, int pivotVal) {
    return sort(source, pivotVal, false);
  }

  private static int[] sort(int[] source, int pivotVal, boolean isLeft) {
    int[] subArray = new int[source.length - 1];
    int j = 0;
    for (int value : source) {
      boolean condition = isLeft && value < pivotVal || !isLeft && value > pivotVal;
      if (condition) {
        subArray[j++] = value;
      }
    }
    return Arrays.copyOf(subArray, j);
  }

  private static int[] combineList(int[] less, int pivotVal, int[] greater) {
    int[] a1 = ArrayUtils.add(less, pivotVal);
    return ArrayUtils.addAll(a1, greater);
  }

}