17-归并排序

 

package cn.sun.it.review;

import java.util.Arrays;

public class MergeSort {

    public static void main(String[] args) {
        int[] arr = {49,38,65,97,76,13,27};
        mergeSort(arr,0,arr.length-1);
        System.out.println(Arrays.toString(arr));
    }
    
    private static void mergeSort(int[] arr, int low, int high) {
        if(low < high){
            int mid = (low+high)/2;
            mergeSort(arr,low,mid);
            mergeSort(arr,mid+1,high);
            merge(arr,low,mid,high);
        }
    }

    // 归并操作
    private static void merge(int[] arr, int low, int mid, int high) {
        int i,j,k;
        int n1 = mid-low+1;
        int n2 = high-mid;
        int[] arr1 = new int[n1];
        int[] arr2 = new int[n2];
        for(i=0;i<n1;i++){
            arr1[i] = arr[low+i];
        }
        for(j=0;j<n2;j++){
            arr2[j] = arr[mid+1+j];
        }
        i=0;
        j=0;
        k = low;
        while(i<n1 && j<n2){
            if(arr1[i] <= arr2[j]){
                arr[k] = arr1[i++];
            }else{
                arr[k] = arr2[j++];
            }
            k++;
        }
        while(i<n1){
            arr[k++] = arr1[i++];
        }
        while(j<n2){
            arr[k++] = arr2[j++];
        }
    }

}