归并排序 迭代版

自学记录

public class MergeSort {    public static void main(String[] args){        int[] b={4,4,1,2,-9,10,101,2,23,9,-40,13,14,5,-8,2,1};        mergeSort(b);        SortTest.show(b);    }    public static void mergeSort(int[] a){        int low,mid,high,step=1,len=a.length;        //step不能大于等于区间长度,只能小于;        while (step<len){            low=0;//从头开始找            // low +step-1+1<=length-1,保证high存在,若连长度为到mid为1的high值都越界了,就不执行循环,例如 (0,1),(2,3),4            while (low+step<len){                mid=low+step-1;                high=mid+step;//mid+1+step-1                if(high>len-1){ //high别越界了                    high=len-1;                }                merge(a,low,mid,high);                low=high+1;            }            step*=2;//一步两,两步四个...        }    }    public static void merge(int[] arr, int low, int mid ,int high){        int i=low,j=mid+1,k=0;        int[] temp = new int[high-low+1];//临时矩阵;        while (i<=mid && j<=high){            if(arr[i]<=arr[j]){         //比较大小;                temp[k++]=arr[i++];            }            else{                temp[k++]=arr[j++];            }        }        while(i<=mid){            temp[k++]=arr[i++];//把剩下的补齐        }        while (j<=high){            temp[k++]=arr[j++];        }        for(i=low,k=0;i<=high;i++,k++){            arr[i]=temp[k];//写回去;        }    }}