Java常见排序算法之归并排序

public class 归并排序 {
    /**
     * 合并两个有序数组
     *
     * @param array1
     * @param array2
     * @return
     */
    public static int[] mergeArray(int[] array1, int[] array2){
        int[] tmp = new int[array1.length+array2.length];
        int i = 0;
        int s1 = 0;
        int s2 = 0;
        int e1 = array1.length-1;
        int e2 = array2.length-1;
        while(s1 <= e1 && s2 <= e2){
            if(array1[s1] <= array2[s2]){
                tmp[i++] = array1[s1++];
            }else{
                tmp[i++] = array2[s2++];
            }
        }
        while(s1 <= e1){
            tmp[i++] = array1[s1++];
        }
        while (s2 <= e2){
            tmp[i++] = array2[s2++];
        }
        return tmp;
    }


    /**
     * 归并排序(递归）
     * 时间复杂度：O(n*logn)
     * 空间复杂度：O(n)
     * 稳定性：稳定
     *
     * 学过的排序只有三个排序是稳定的：冒泡 插入 归并
     * @param array
     */
    public static void mergeSort1(int[] array){
        mergeSortFunc(array, 0, array.length-1);
    }
    public static void mergeSortFunc(int[] array, int low, int high){
        if(low >= high){
            return;
        }
        int mid = low + ((high-low)>>>2);
        mergeSortFunc(array, low, mid);
        mergeSortFunc(array, mid+1, high);
        merge(array, low, high, mid);
    }
    public static void merge(int[] array, int low, int high, int mid) {
        int[] tmp = new int[high-low+1];
        int i = 0;
        int s1 = low;
        int s2 = mid+1;
        int e1 = mid;
        int e2 = high;
        while(s1 <= e1 && s2 <= e2){
            if(array[s1] <= array[s2]){//   <=稳定的排序
                tmp[i++] = array[s1++];
            }else{
                tmp[i++] = array[s2++];
            }
        }
        while(s1 <= e1){
            tmp[i++] = array[s1++];
        }
        while (s2 <= e2){
            tmp[i++] = array[s2++];
        }
        for (int j = 0; j < tmp.length; j++) {
            array[j+low] = tmp[j];
        }
    }

    public static void mergeSort2(int[] array){
        int nums = 1;//每组数的个数
        while(nums < array.length){
            for (int i = 0; i < array.length; i += 2*nums) {
                int left = i;
                int mid = left + nums - 1;
                if(mid >= array.length){
                    mid = array.length-1;
                }
                int right = nums + mid;
                if(right >= array.length){
                    right = array.length-1;
                }
                merge(array, left, right, mid);
            }
            nums *= 2;
        }
    }

    public static void main(String[] args) {
        int[] array1 = {1,3,5,7,9,10};
        int[] array2 = {0,2,3,4,5,6,7,8};
        int[] array = {2,4,5,3,5,67,5,4,34,5};
        mergeSort2(array);
        System.out.println(Arrays.toString(array));
    }
}