Sorting algorithm Five: merge sort

Ranking Algorithm Efficiency after fast discharge, typically for the disorder in general, but each child relatively orderly series

Idea: using a very typical application of divide and conquer. The combined sequence has been ordered, fully ordered sequence; i.e., each first ordered sequence, and then ordered to make inter-segment sequences

The average time complexity is nlog2n, spatial complexity is n, stable

public class Merge {
    /**
     * 对数组进行排序
     * @param arr：要排序的数组
     * @param left：数组的开始下标
     * @param right：数组的终止下标
     */
    public void sort(int[] arr,int left,int right){
        if(left==right) return;
        int mid=(left+right)/2;               //记录中间位置下标,将数组分成两半
        sort(arr,left,mid);                   //左边排序
        sort(arr,mid+1,right);            //右边排序
        merge(arr,left,mid+1,right);
    }

    /**
     *归并排序
     * @param arr:要排序的数组
     * @param leftptr:排序的左指针
     * @param rightptr：排序的右指针
     * @param bound：边界
     */
    public void merge(int[] arr , int leftptr , int rightptr , int bound){
        //int mid=rightptr-1;                  //记录中间位置的下标
        int[] temp=new int[bound-leftptr+1];        //用于存放排好序的数组
        int i=leftptr;                               //记录前半截数组的初始下标
        int j=rightptr;                           //记录后半截数组的初始下标
        int k=0;                               //记录新数组的第一个下标
        while (i<rightptr&&j<=bound){         //当前半截数组与后半截数组都有未排好序的数时
            if(arr[i]<=arr[j]){                 //判断前半截数组与后半截数组值的大小
                temp[k]=arr[i];                //交换，将小的数存放在新的数组中
                i++;
                k++;
            }else{
                temp[k]=arr[j];
                j++;
                k++;
            }
        }
        while (i<rightptr) {            //如果一方已排好序而另一方还有数剩，则说明剩下的数已排好序，直接存放在新数组中
            temp[k]=arr[i];
            i++;
            k++;
        }
        while (j<=bound){
            temp[k]=arr[j];
            j++;
            k++;
        }
        for(int a=0;a<temp.length;a++){
             arr[leftptr+a]=temp[a];
        }
    }


}

The main function:

public class main {
    public static void main(String[] args) {
        int[] arr={4,5,7,3,5,42,6,1,2,1,75};
        Merge merge=new Merge();
        merge.sort(arr,0,arr.length-1);
        for (int i=0;i<arr.length;i++){
            System.out.print(arr[i]+" ");
        }
    }

}

Output: 1123455674275