# 替代排序 > 原文： [https://www.geeksforgeeks.org/alternative-sorting/](https://www.geeksforgeeks.org/alternative-sorting/) 給定一個整數數組，以第一個元素為第一個最大值，第二個元素為第一個最小值的方式打印該數組，依此類推。 **示例**： ``` Input : arr[] = {7, 1, 2, 3, 4, 5, 6} Output : 7 1 6 2 5 3 4 Input : arr[] = {1, 6, 9, 4, 3, 7, 8, 2} Output : 9 1 8 2 7 3 6 4 ``` 一個**簡單解決方案**是先打印最大元素，然后再打印最小值，然后再打印第二個最大值，依此類推。 該方法的時間復雜度為 `O(n^2)`。 **有效解決方案**涉及以下步驟。 1）使用`O(N log N)`算法對輸入數組進行排序。 2）我們在排序數組中維護兩個指針，一個從頭開始，一個從頭結束。 我們也可以打印由兩個指針指向的元素，并將它們彼此相對移動。 ## C++ ```cpp // C++ program to print an array in alternate // sorted manner. #include <bits/stdc++.h> using namespace std; // Function to print alternate sorted values void alternateSort(int arr[], int n) { ????// Sorting the array ????sort(arr, arr+n); ????// Printing the last element of array? ????// first and then first element and then? ????// second last element and then second? ????// element and so on. ????int i = 0, j = n-1; ????while (i < j) { ????????cout << arr[j--] << " "; ????????cout << arr[i++] << " "; ????} ????// If the total element in array is odd? ????// then print the last middle element. ????if (n % 2 != 0) ????????cout << arr[i]; } // Driver code int main() { ????int arr[] = {1, 12, 4, 6, 7, 10}; ????int n = sizeof(arr)/sizeof(arr[0]); ????alternateSort(arr, n); ????return 0; } ``` ## Java ```java // Java program to print an array in alternate // sorted manner import java.io.*; import java.util.Arrays; class AlternativeString { ????// Function to print alternate sorted values ????static void alternateSort(int arr[], int n) ????{ ????????Arrays.sort(arr); ????????// Printing the last element of array? ????????// first and then first element and then? ????????// second last element and then second? ????????// element and so on. ????????int i = 0, j = n-1; ????????while (i < j) { ????????????System.out.print(arr[j--] + " "); ????????????System.out.print(arr[i++] + " "); ????????} ????????// If the total element in array is odd? ????????// then print the last middle element. ????????if (n % 2 != 0) ????????????System.out.print(arr[i]); ????} ????/* Driver program to test above functions */ ????public static void main (String[] args) ????{ ????????int arr[] = {1, 12, 4, 6, 7, 10}; ????????int n = arr.length; ????????alternateSort(arr, n); ????} } /*This code is contributed by Prakriti Gupta*/ ``` ## Python3 ```py # Python 3 program to print an array # in alternate sorted manner. # Function to print alternate sorted # values def alternateSort(arr, n): ????# Sorting the array ????arr.sort()? ????# Printing the last element of array? ????# first and then first element and then? ????# second last element and then second? ????# element and so on. ????i = 0 ????j = n-1 ????while (i < j):? ????????print(arr[j], end =" ") ????????j-= 1 ????????print(arr[i], end =" ") ????????i+= 1 ????# If the total element in array is odd? ????# then print the last middle element. ????if (n % 2 != 0): ????????print(arr[i])? # Driver code arr = [1, 12, 4, 6, 7, 10]? n = len(arr) alternateSort(arr, n)? # This code is contributed by # Smitha Dinesh Semwal ``` ## C# ```cs // C# program to print an array in alternate // sorted manner using System; class AlternativeString { ????// Function to print alternate sorted values ????static void alternateSort(int[] arr, int n) ????{ ????????Array.Sort(arr); ????????// Printing the last element of array ????????// first and then first element and then ????????// second last element and then second ????????// element and so on. ????????int i = 0, j = n - 1; ????????while (i < j) { ????????????Console.Write(arr[j--] + " "); ????????????Console.Write(arr[i++] + " "); ????????} ????????// If the total element in array is odd ????????// then print the last middle element. ????????if (n % 2 != 0) ????????????Console.WriteLine(arr[i]); ????} ????/* Driver program to test above functions */ ????public static void Main() ????{ ????????int[] arr = { 1, 12, 4, 6, 7, 10 }; ????????int n = arr.Length; ????????alternateSort(arr, n); ????} } // This article is contributed by vt_m. ``` ## PHP ```php <?php // PHP program to print an array in? // alternate sorted manner. // Function to print alternate // sorted values function alternateSort($arr, $n) { ????// Sorting the array ????sort($arr); ????// Printing the last element? ????// of array? first and then? ????// first element and then second? ????// last element and then second?? ????// element and so on. ????$i = 0; ????$j = $n - 1; ????while ($i < $j) ????{ ????????echo $arr[$j--]." "; ????????echo $arr[$i++]." "; ????} ????// If the total element in array?? ????// is odd then print the last? ????// middle element. ????if ($n % 2 != 0) ????????echo $arr[$i]; } // Driver code $arr= array(1, 12, 4, 6, 7, 10); $n = sizeof($arr) / sizeof($arr[0]); alternateSort($arr, $n); // This code is contributed by Mithun Kumar ?> ``` **輸出**： ``` 12 1 10 4 7 6 ``` **時間復雜度**：`O(N log N)` **輔助空間**：`O(1)`