787. 归并排序

787. 归并排序 - AcWing题库

Question

Content

给定你一个长度为 n 的整数数列。

请你使用归并排序对这个数列按照从小到大进行排序。

并将排好序的数列按顺序输出。

输入格式

输入共两行，第一行包含整数 n 。

第二行包含 n 个整数（所有整数均在 1 ~ $10^9$ 范围内），表示整个数列。

输出格式

输出共一行，包含 n 个整数，表示排好序的数列。

数据范围

1≤n≤100000

输入样例：

5
3 1 2 4 5

输出样例：

1 2 3 4 5

Solution

Java

import java.util.Scanner;
import java.util.stream.IntStream;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int[] arr = IntStream.range(0, n)
                .map(i -> scanner.nextInt()).toArray();

        int[] mergeSort = mergeSort(arr, 0, n - 1);

        IntStream.range(0, n).mapToObj(i -> mergeSort[i] + " ")
                .forEach(System.out::print);
    }

    private static int[] mergeSort(int[] arr, int left, int right) {
        if (left >= right) {
            return arr;
        }

        int mid = (left + right) >> 1;

        arr = mergeSort(arr, left, mid);
        arr = mergeSort(arr, mid + 1, right);

        int[] temp = new int[right - left + 1];
        int i = left, 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) {
            temp[k++] = arr[i++];
        }

        while (j <= right) {
            temp[k++] = arr[j++];
        }

        for (i = left, j = 0; i <= right; i++, j++) {
            arr[i] = temp[j];
        }

        return arr;
    }

}

Summary

The program efficiently implements the Merge Sort algorithm, breaking down the sorting process into smaller subproblems and merging them to achieve a sorted array. It uses recursion to handle the divide-and-conquer strategy and temporary arrays for merging. The sorted array is then printed as the final output.