题目描述

归并排序

样例

import java.io.BufferedInputStream;
import java.util.Scanner;

/*
   中间分开：对左右两边都递归排序
   开一个结果数组，双指针分别指向左右区间的最小值(也就是最左位置)
   比较大小后放入结果数组，判断是否还有剩下的，有就全部
*/

public class Main {
    private static int[] mergeSort(int[] arr, int left, int right) {
        if (left >= right) {
            return arr;
        }
        int mid = (left + right) / 2;
        arr = mergeSort(arr, left, mid);
        arr = mergeSort(arr, mid + 1, right);
        int[] temp = new int[right - left + 1];
        int i = left;
        int j = mid + 1;
        int k = 0;
        while (i <= mid && j <= right) {
            if (arr[i] <= arr[j]) {
                temp[k++] = arr[i++];
            } else {
                temp[k++] = arr[j++];
            }
        }
        while (i <= mid) {//判断左半边的数组还有没有剩
            temp[k++] = arr[i++];
        }
        while (j <= right) {//判断右半边的数组还有没有剩
            temp[k++] = arr[j++];
        }
        for (i = left, j = 0; i <= right; i++, j++) {//复制回自己的数组
            arr[i] = temp[j];
        }
        return arr;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(new BufferedInputStream(System.in));
        int n = in.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = in.nextInt();
        }

        mergeSort(arr, 0, n - 1);

        for (int i = 0; i < n; i++) {
            System.out.print(arr[i] + " ");
        }

    }
}