给定一个未排序的数组，重新排列数组，使奇数索引处的数字大于上一个偶数索引处的数字。可能有多个输出，我们需要打印其中一个。
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注： 索引是基于数组的，所以它总是从0开始。
例如：
Input : arr[] = {5, 2, 3, 4}Output : arr[] = {2, 5, 3, 4}Input : arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9}Output : arr[] = {1, 3, 2, 5, 4, 7, 6, 9, 8}
如果给定的数组长度为偶数，则可以在一次运行中完成。对于每对邻居，将最大值放在奇数位置，将最小值放在偶数位置。所以我们从一开始就开始一个循环，比较每两个元素。比方说 6，5，4，3，2，1会给我们5，6，3，4，1，2 如果数组的长度是奇数，比如6，5，4，3，2，1，100，那么它就有点复杂了，我们需要再次运行第二个反向循环，但从最后一个元素开始。所以，第一个循环之后的6，5，4，3，2，1100将是5，6，3，4，1，2，100，第二个循环之后的5，6，3，4，1，100，2
C++
// C++ program to rearrange array such that // odd indexed elements are greater. #include<bits/stdc++.h> using namespace std; void rearrange( int arr[], int n) { // Common code for odd and even lengths for ( int i=0; i<n-1; i=i+2) { if (arr[i] > arr[i+1]) swap(arr[i], arr[i+1]); } // If length is odd if (n & 1) { for ( int i=n-1; i>0; i=i-2) if (arr[i] > arr[i-1]) swap(arr[i], arr[i-1]); } } /* Utility that prints out an array on a line */ void printArray( int arr[], int size) { for ( int i=0; i < size; i++) printf ( "%d " , arr[i]); printf ( "" ); } /* Driver function to test above functions */ int main() { int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9}; int n = sizeof (arr)/ sizeof (arr[0]); cout << "Before rearranging" ; printArray(arr, n); rearrange(arr, n); cout << "After rearranging" ; printArray(arr, n); return 0; } |
JAVA
// Java program to rearrange array such that // odd indexed elements are greater. import java.util.Arrays; class GFG { // Utility function to Swap two variables public static void swap( int [] arr, int i, int j) { int temp = arr[i]; arr[i] = arr[j]; arr[j] = temp; } // method to rearrange array such that // odd indexed elements are greater. public static void Rearrange( int [] arr, int n) { // Common code for odd and even lengths for ( int i = 0 ; i < n - 1 ; i = i + 2 ) { if (arr[i] > arr[i + 1 ]) swap(arr, i, i + 1 ); } // If length is odd if ((n & 1 ) > 0 ) { for ( int i = n - 1 ; i > 0 ; i = i - 2 ) if (arr[i] > arr[i - 1 ]) swap(arr, i, i - 1 ); } } // Driver Method public static void main(String[] args) { int [] arr = { 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 }; System.out.println( "Before rearranging" ); System.out.println(Arrays.toString(arr)); Rearrange(arr, arr.length); System.out.println( "After rearranging" ); System.out.println(Arrays.toString(arr)); } } /* This code is contributed by Mr. Somesh Awasthi */ |
Python3
# Python 3 program to rearrange array such # that odd indexed elements are greater. def rearrange(arr, n): # Common code for odd and even lengths for i in range ( 0 , n - 1 , 2 ): if (arr[i] > arr[i + 1 ]): temp = arr[i] arr[i] = arr[i + 1 ] arr[i + 1 ] = temp # If length is odd if (n & 1 ): i = n - 1 while (i > 0 ): if (arr[i] > arr[i - 1 ]): temp = arr[i] arr[i] = arr[i - 1 ] arr[i - 1 ] = temp i - = 2 # Utility that prints out an # array on a line def printArray(arr, size): for i in range ( 0 , size, 1 ): print (arr[i], end = " " ) print ( "" ) # Driver Code if __name__ = = '__main__' : arr = [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ] n = len (arr) print ( "Before rearranging" ) printArray(arr, n) rearrange(arr, n) print ( "After rearranging" ) printArray(arr, n) # This code is contributed by # Surendra_Gangwar |
C#
// C# program to rearrange // array such that odd // indexed elements are // greater. using System; class GFG { // Utility function to // Swap two variables public static void swap( int [] arr, int i, int j) { int temp = arr[i]; arr[i] = arr[j]; arr[j] = temp; } // method to rearrange // array such that odd // indexed elements are // greater. public static void Rearrange( int [] arr, int n) { // Common code for odd // and even lengths for ( int i = 0; i < n - 1; i = i + 2) { if (arr[i] > arr[i + 1]) swap(arr, i, i + 1); } // If length is odd if ((n & 1) > 0) { for ( int i = n - 1; i > 0; i = i - 2) if (arr[i] > arr[i - 1]) swap(arr, i, i - 1); } } // Driver Code static void Main() { int [] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9}; Console.WriteLine( "Before rearranging" ); for ( int i = 0; i < arr.Length; i++) Console.Write(arr[i] + " " ); Rearrange(arr, arr.Length); Console.WriteLine( "After rearranging" ); for ( int i = 0; i < arr.Length; i++) Console.Write(arr[i] + " " ); } } // This code is contributed // by Sam007 |
PHP
<?php // PHP program to rearrange array such that // odd indexed elements are greater. function rearrange(& $arr , $n ) { // Common code for odd and even lengths for ( $i = 0; $i < $n - 1; $i = $i + 2) { if ( $arr [ $i ] > $arr [ $i + 1]) { $temp = $arr [ $i ]; $arr [ $i ] = $arr [ $i + 1]; $arr [ $i + 1] = $temp ; } } // If length is odd if ( $n & 1) { for ( $i = $n - 1; $i > 0; $i = $i - 2) if ( $arr [ $i ] > $arr [ $i - 1]) { $temp = $arr [ $i ]; $arr [ $i ] = $arr [ $i - 1]; $arr [ $i - 1] = $temp ; } } } // Utility that prints out an array on a line function printArray(& $arr , $size ) { for ( $i = 0; $i < $size ; $i ++) echo $arr [ $i ] . " " ; echo "" ; } // Driver Code $arr = array (1, 2, 3, 4, 5, 6, 7, 8, 9); $n = sizeof( $arr ); echo "Before rearranging" ; printArray( $arr , $n ); rearrange( $arr , $n ); echo "After rearranging" ; printArray( $arr , $n ); // This code is contributed by ita_c ?> |
Javascript
<script> // Javascript program to rearrange array such that // odd indexed elements are greater. // Utility function to Swap two variables function swap(arr,i,j) { let temp = arr[i]; arr[i] = arr[j]; arr[j] = temp; } // method to rearrange array such that // odd indexed elements are greater. function Rearrange(arr,n) { // Common code for odd and even lengths for (let i = 0; i < n - 1; i = i + 2) { if (arr[i] > arr[i + 1]) swap(arr, i, i + 1); } // If length is odd if ((n & 1) > 0) { for (let i = n - 1; i > 0; i = i - 2) if (arr[i] > arr[i - 1]) swap(arr, i, i - 1); } } // Driver Method let arr=[ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]; document.write( "Before rearranging<br>" ); for (let i=0;i<arr.length;i++) { document.write(arr[i]+ " " ); } document.write( "<br>" ) Rearrange(arr, arr.length); document.write( "After rearranging<br>" ); for (let i=0;i<arr.length;i++) { document.write(arr[i]+ " " ); } // This code is contributed by avanitrachhadiya2155 </script> |
输出：
Before rearranging1 2 3 4 5 6 7 8 9 After rearranging1 3 2 5 4 7 6 9 8
时间复杂性： O（n）
辅助空间： O（1）
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