算法——希爾排序

 希爾排序是插入排序的進化版，在進行比交換位置時以增量進行交換或移動；經過比較相距必定間隔的元素來工做；各趟比較所用的距離隨着算法的進行而減少，直到只比相鄰元素的最後一趟排序爲止，所以有時也叫縮減增量排序

  直接上代碼吧（可能並非最好的例子）：

 public void shellSort(){
        int[] a = {81,94,11,96,12,35,17,95,28,58,41,75,15};
        System.out.println(Arrays.toString(a));
        int j;
        for (int gap = a.length/2; gap > 0 ; gap /= 2) {
            for (int i = gap; i < a.length; i++) {
                int tmp = a[i];
                for (j = i; j >= gap && tmp < a[j-gap] ; j -= gap) {
                    a[j] = a[j-gap];
                }
                a[j] = tmp;
            }
        }
        System.out.println(Arrays.toString(a));
    }

 以gap=3爲例，結合代碼：

public void shellSort(){
        int[] a = {15, 94, 11, 58, 12, 35, 17, 95, 28, 96, 41, 75, 81};//gap=3以前的數組
        System.out.println(Arrays.toString(a));
        int j;
        for (int gap = a.length/2; gap > 0 ; gap /= 2) {
            for (int i = gap; i < a.length; i++) {
                int tmp = a[i];//tmp
                for (j = i; j >= gap && tmp < a[j-gap] ; j -= gap) {
                    a[j] = a[j-gap];
                   //15, 94, 11, 58, 94, 35, 17, 95, 28, 96, 41, 75, 81
                  //15, 12, 11, 58, 94, 35, 58, 95, 28, 96, 41, 75, 81
                   //15, 12, 11, 17, 94, 35, 58, 95, 35, 96, 41, 75, 81
                   //15, 12, 11, 17, 94, 28, 58, 95, 35, 96, 95, 75, 81
                    //15, 12, 11, 17, 94, 28, 58, 94, 35, 96, 95, 75, 81
                     //15, 12, 11, 17, 41, 28, 58, 94, 35, 96, 95, 75, 96
                }
                a[j] = tmp;
            }
　　　　　　//gap=3以後的數組：[15, 12, 11, 17, 41, 28, 58, 94, 35, 81, 95, 75, 96]
        }
        System.out.println(Arrays.toString(a));
    } 

希爾排序與插入排序不一樣的是：希爾排序是增量式的不想普通的插入排序一個一個的往前比較，而是按增量進行大間距的移動或交換