归并算法

import java.util.Arrays;   
  
/**  
 * java归并算法实现<br>  
 *   
 * @author JAVA世纪网(java2000.net, laozizhu.com)  
 */  
public class Test {   
  final static int MAXVALUE = 10000;   
  
  static int[] L;   
  
  static int[] R;   
  
  public static void Merge(int[] A, int p, int q, int r) {   
    int n1 = q - p;   
    int n2 = r - q + 1;   
    L = new int[n1 + 1];   
    R = new int[n2 + 1];   
    for (int i = 0; i < n1; i++) {   
      L[i] = A[p + i];   
    }   
    for (int j = 0; j < n2; j++) {   
      R[j] = A[q + j];   
    }   
    L[n1] = MAXVALUE;   
    R[n2] = MAXVALUE;   
    int i = 0, j = 0;   
    for (int k = p; k <= r; k++) {   
      if (L[i] <= R[j]) {   
        A[k] = L[i];   
        i++;   
      } else {   
        A[k] = R[j];   
        j++;   
      }   
    }   
  }   
  
  public static void MergeSort(int[] A, int p, int r) {   
    int q;   
    if (p < r) {   
      q = (p + r) / 2;   
      MergeSort(A, p, q);   
      MergeSort(A, q + 1, r);   
      Merge(A, p, q + 1, r);   
    }   
  }   
  
  public static void main(String[] args) {   
    int[] inputArray = { 1, 3, 2, 6, 5, 2, 4, 7, 1, 3, 2, 6, 5, 2, 4, 7, 1, 3, 2, 6, 5, 2, 4, 7, 1,   
        3 };   
    // 方法1   
    MergeSort(inputArray, 0, inputArray.length - 1);   
    System.out.println(Arrays.toString(inputArray));   
    Integer[] inputArray2 = { 1, 3, 2, 6, 5, 2, 4, 7, 1, 3, 2, 6, 5, 2, 4, 7, 1, 3, 2, 6, 5, 2, 4,   
        7, 1, 3 };   
    // 方法2   
    new MergeSort().sort(inputArray2);   
    System.out.println(Arrays.toString(inputArray2));   
  }   
}   
  
class MergeSort {   
  private Comparable[] bridge;   
  
  /**  
   * *利用归并排序算法对数组obj进行排序  
   */  
  public void sort(Comparable[] obj) {   
    if (obj == null) {   
      throw new NullPointerException("The param can not be null!");   
    }   
    bridge = new Comparable[obj.length];// 初始化中间数组   
    mergeSort(obj, 0, obj.length - 1); // 归并排序   
    bridge = null;   
  }   
  
  /**  
   * 将下标从left到right的数组进行归并排序  
   *   
   * @param obj 要排序的数组的句柄  
   * @param left 要排序的数组的第一个元素下标  
   * @param right 要排序的数组的最后一个元素的下标  
   */  
  private void mergeSort(Comparable[] obj, int left, int right) {   
    if (left < right) {   
      int center = (left + right) / 2;   
      mergeSort(obj, left, center);   
      mergeSort(obj, center + 1, right);   
      merge(obj, left, center, right);   
    }   
  }   
  
  /**  
   * *将两个对象数组进行归并，并使归并后为升序。归并前两个数组分别有序  
   *   
   * @param obj 对象数组的句柄  
   * @param left 左数组的第一个元素的下标  
   * @param center 左数组的最后一个元素的下标  
   * @param right 右数组的最后一个元素的下标  
   */  
  private void merge(Comparable[] obj, int left, int center, int right) {   
    int mid = center + 1;   
    int third = left;   
    int tmp = left;   
    while (left <= center && mid <= right) { // 从两个数组中取出小的放入中间数组   
      if (obj[left].compareTo(obj[mid]) <= 0) {   
        bridge[third++] = obj[left++];   
      } else  
        bridge[third++] = obj[mid++];   
    }   
    // 剩余部分依次置入中间数组   
    while (mid <= right) {   
      bridge[third++] = obj[mid++];   
    }   
    while (left <= center) {   
      bridge[third++] = obj[left++];   
    }   
    // 将中间数组的内容拷贝回原数组   
    copy(obj, tmp, right);   
  }   
  
  /**  
   * *将中间数组bridge中的内容拷贝到原数组中  
   *   
   * @param obj 原数组的句柄  
   * @param left 要拷贝的第一个元素的下标  
   * @param right 要拷贝的最后一个元素的下标  
   */  
  private void copy(Comparable[] obj, int left, int right) {   
    while (left <= right) {   
      obj[left] = bridge[left];   
      left++;   
    }   
  }   
}