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归并排序实现(JAVA)

烟中雯城 2022-01-10 阅读 44

归并排序采用的是分治思想

public class Main {

    public static void main(String[] args) {
        int []arr = {4,5,6,2,1,9};
        int left = 0;
        int right = arr.length-1;
        int[] temp = new int[arr.length];
        asort(arr,left,right,temp);
        System.out.println(Arrays.toString(temp));
    }

    /**
     * 归并查找
     * @param arr
     * @param left
     * @param right
     * @param mid
     * @return
     */
    public static void mergeSort(int[] arr,int left,int right,int mid,int[] temp){
        int i = left;
        int n = left;
        int j = mid+1;
        while (n<=mid && j<=right && i<=right){
            if(arr[n]>arr[j]){
                //左边数>右边数,存储右边数,左边数不变,右边数索引增加
                temp[i++] = arr[j++];
            }else{
                //左边数<右边数,存储左边数,右边数不变,左边数索引增加
                temp[i++] = arr[n++];
            }
        }
        //右边全部比较存储完毕,左边没比完,则直接将左边的放入数组中
        while(n<=mid && i<=right){
            temp[i++] = arr[n++];
        }
        //左边全部比较存储完毕,右边没比完,则直接将右边的放入数组中
        while(j<=right && i<=right){
            temp[i++] = arr[j++];
        }
        //修改原数组
        for(int m = left;m<=right;m++){
            arr[m]=temp[m];
        }
    }

    /**
     * 递归执行
     * @param arr
     * @param left
     * @param right
     * @param temp
     */
    public static void asort(int[] arr,int left,int right,int[] temp){
            if(right>left){
                int mid = (left+right)/2;
                asort(arr,left,mid,temp);
                asort(arr,mid+1,right,temp);
                mergeSort(arr,left,right,mid,temp);
            }else{
                temp[0]=arr[0];
            }
    }

}
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