Que03|787. 归并排序

题目：787. 归并排序 - AcWing题库

思路：

代码实现：

import java.util.*;
public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
        }
        mergeSort(arr, 0, n - 1);
        for (int i = 0; i < n; i++) {
            System.out.print(arr[i] + " ");
        }
    }
    public static void mergeSort(int[] arr, int l, int r) {
        if (l >= r) return;
        int mid = (l + r) / 2;
        mergeSort(arr, l, mid);
        mergeSort(arr, mid + 1, r);
        
        int[] temp = new int[r - l + 1];
        int k = 0, i = l, j = mid + 1;
        while (i <= mid && j <= r) {
            if (arr[i] <= arr[j]) {
                temp[k++] = arr[i++];
            } else {
                temp[k++] = arr[j++];
            }
        }
        while (i <= mid) {
            temp[k++] = arr[i++];
        }
        while (j <= r) {
            temp[k++] = arr[j++];
        }
        for (i = l, j = 0; i <= r; i++, j++) {
            arr[i] = temp[j];
        }
    }
}