归并排序（比希尔还要快）

代码

public class MergeSort {

  public static void main(String[] args) {
//    int[] arr = {8,4,5,7,1,3,2,6};
//    int[] temp = new int[arr.length];
//    System.out.println("排序前：" +Arrays.toString(arr));
//    mergeSort(arr, 0, arr.length - 1, temp);
//    System.out.println("排序后：" +Arrays.toString(arr));
    int[] arr = new int[80000000];
    int[] temp = new int[arr.length];
    for (int i = 0; i < arr.length; i++) {
      //生成一个【0，8000000】的数
      arr[i] = (int)(Math.random() * 8000000);
    }
    long start = System.currentTimeMillis();
    mergeSort(arr, 0, arr.length - 1, temp);
    long end = System.currentTimeMillis();
    System.out.println("总共花费：" + (end - start));
  }
  
  public static void mergeSort(int[] arr,int left,int right,int[] temp){
    if(left < right){
      int mid = (left + right) / 2;
      mergeSort(arr, left, mid, temp);
      mergeSort(arr, mid + 1, right, temp);
      merge(arr, left, mid, right, temp);
    }
  }
  
  public static void merge(int[] arr,int left,int mid,int right,int[] temp){
    int i = left;
    int j = mid + 1;
    int t = 0;//指向temp的当前索引
    while(i <= mid && j <= right){
      if(arr[i] < arr[j]){
        temp[t] = arr[i];
        i += 1;
        t += 1;
      }else{
        temp[t] = arr[j];
        j += 1;
        t += 1;
      }
      
    }
    while(i <= mid){
      temp[t] = arr[i];
      i += 1;
      t += 1;
    }
    while(j <= right){
      temp[t] = arr[j];
      j += 1;
      t += 1;
    }
    t = 0;
    int tempLeft = left;
    while(tempLeft <= right){
      arr[tempLeft] = temp[t];
      t += 1;
      tempLeft += 1;
    }
  }
}

效率

//8000 0000 15156ms
    //800 0000 1378ms
    //80 0000 1118ms
    //8 0000 28ms