归并排序

/**
 * @Description
 * @Author admin
 * @Date 2021/1/7 16:40
 * @Version 1.0
 */
public class Main01 {

    public static int count=0;

    public static void main(String[] args) {
        int[] arr = {1,9,3,22,10,8,4,2,99,31,3332,2,19,322,544,29,103,56};
        System.out.println(arrstr(arr));

        sort(arr);

        System.out.println(arrstr(arr));

        System.out.println("count:"+count);
    }

    public static void sort(int[] arr){
        int L = 0;
        int R = arr.length-1;
        process(arr,L,R);//全部有序

    }


    public static void process(int[] arr,int L,int R){
        String baselog = "process("+(L)+","+R+") ";
        System.out.println(arrstr(arr)+"----L:"+L+",R:"+R);

        if(L==R){
            System.out.println(baselog+"只有一个元素L:"+L+",arr[L]:"+arr[L]);
            return;//只有一个元素，本身就是有序的, 表示当前分组已变成有序的了
        }
        int M = L+((R-L)>>1); //取出中点，继续拆分
        System.out.println(baselog+"M:"+M);

        System.out.println(baselog+"左边开始排序，范围：("+L+","+M+")");
        process(arr,L,M);//左边有序

        System.out.println(baselog+"右边开始排序，范围：("+(M+1)+","+R+")");
        process(arr,M+1,R);//右边有序

        System.out.println(baselog+"开始合并排序，范围：("+L+","+M+"],"+R+")");
        merge(arr,L,M,R);//合并有序
    }

    public static void merge(int[] arr,int L, int M, int R){

        String baselog = "merge("+L+","+M+"],"+R+") ";
        int[] result = new int[R-L+1];

        int LP = L;
        int RP = M+1;
        System.out.println(baselog+"LP："+LP+",RP:"+RP);

        int i=0;
        while(LP<=M && RP<=R){
            count++;
            result[i++] = arr[LP]<arr[RP]?arr[LP++]:arr[RP++];
        }

        while (LP<=M){
            count++;
            result[i++] =  arr[LP++];
        }

        while (RP<=R){
            count++;
            result[i++] =  arr[RP++];
        }
        for(int k=L;k<=R;k++){
            count++;
            arr[k]=result[k-L]; //result数组的起始位置0 对应原数据是L，原数组 比 result数组多了L的偏移
        }
        System.out.println(baselog+"arrstr(arr)："+arrstr(arr));
        System.out.println(baselog+"arrstr(result):"+arrstr(result));

    }

    public static String arrstr(int[] arr){
        StringBuffer sb = new StringBuffer();

        for(int i: arr){
            sb.append(String.valueOf(i)).append(" ");
        }
       return sb.toString();
    }
}