java 基本算法之归并排序实例代码

public class MergeSort {

  /**
   * 
   *
   *
   * @param args
   */
  public static void main(String[] args) {
    int a[] = { 49, 38, 65, 97, 76, 13, 27, 49, 78, 34, 12, 64, 5, 4, 62,
        99, 98, 54, 56, 17, 18, 23, 34, 15, 35, 25, 53, 51 };

    sort(a, 0, a.length - 1);
    System.out.println(Arrays.toString(a));

  }

  public static void sort(int[] data, int left, int right) {
    if (left < right) {
      // 找出中间索引
      int center = (left + right) / 2;
      // 对左边数组进行递归
      sort(data, left, center);
      // 对右边数组进行递归
      sort(data, center + 1, right);
      // 合并
      merge(data, left, center, right);
    }

  }

  public static void merge(int[] data, int left, int center, int right) {
    int[] tmpArr = new int[data.length];
    int mid = center + 1;
    // third记录中间数组的索引
    int third = left;
    int tmp = left;
    while (left <= center && mid <= right) {
      // 从两个数组中取出最小的放入中间数组
      if (data[left] <= data[mid]) {
        tmpArr[third++] = data[left++];
      } else {
        tmpArr[third++] = data[mid++];
      }

    }

    // 剩余部分依次放入中间数组
    while (left <= center) {
      tmpArr[third++] = data[left++];
    }
    while (mid <= right) {
      tmpArr[third++] = data[mid++];
    }

    // 将中间数组中的内容复制回原数组
    while (tmp <= right) {
      data[tmp] = tmpArr[tmp++];
    }
    System.out.println(Arrays.toString(data));
  }

}