用所有其他最小的数组元素替换每个元素

给定一个由N个整数组成的数组arr [] ，任务是用数组中存在的所有其他元素中的最小元素替换每个元素。

例子：

Input: arr[] = {1, 1, 1, 2} 
Output: 1 1 1 1

Input: arr[] = {4, 2, 1, 3} 
Output: 1 1 2 1  

天真的方法：
最简单的方法是借助嵌套循环为每个元素找到所有剩余元素中的最小元素。

时间复杂度： O(N ² )

高效方法：
想法是维护前缀和后缀min数组。维护leftMin []和rightMin []数组，它们为每个数组元素在左子数组和右子数组中存储最小值。计算完成后，通过存储leftMin [i]和rightMin [i]的最小值来替换原始数组的^第i^个索引。

下面是上述方法的实现：

C++

// C++ program to replace every element
// with the smallest of all other
// array elements
#include
using namespace std;
 
void ReplaceElements(int arr[], int n)
{
     
    // There should be atleast two elements
    if (n < 2)
    {
        cout << (" Invalid Input ");
        return;
    }
 
    // leftMin array stores minimum
    // element of left subarray
    int leftMin[n];
    leftMin[0] = INT_MAX;
 
    // rightMin array stores minimum
    // element of right subarray
    int rightMin[n];
    rightMin[n - 1] = INT_MAX;
 
    for(int i = 1; i < n; i++)
    {
       leftMin[i] = min(leftMin[i - 1], arr[i - 1]);
       rightMin[n - 1 - i] = min(rightMin[n - 1 - i + 1],
                                      arr[n - 1 - i + 1]);
    }
     
    // Update original array with minimum
    // of leftMin[i] and rightMin[i]
    for(int i = 0; i < n; i++)
    {
       arr[i] = min(leftMin[i], rightMin[i]);
    }
 
    // Print the modified array.
    for(int i = 0; i < n; ++i)
    {
       cout << arr[i] << " ";
    }
}
 
// Driver code
int main()
{
    int arr[] = { 1, 2, 3, 2 };
     
    int n = sizeof(arr) / sizeof(arr[0]);
 
    ReplaceElements(arr, n);
}
 
// This code is contributed by chitranayal

Java

// Java program to replace every element
// with the smallest of all other
// array elements
import java.util.*;
 
class GFG {
 
    static void ReplaceElements(int[] arr, int n)
    {
 
        /* There should be atleast two elements */
        if (n < 2) {
            System.out.println(" Invalid Input ");
            return;
        }
 
        // leftMin array stores minimum
        // element of left subarray
        int[] leftMin = new int[n];
        leftMin[0] = Integer.MAX_VALUE;
 
        // rightMin array stores minimum
        // element of right subarray
        int[] rightMin = new int[n];
        rightMin[n - 1] = Integer.MAX_VALUE;
 
        for (int i = 1; i < n; i++) {
            leftMin[i] = Math.min(leftMin[i - 1],
                                  arr[i - 1]);
            rightMin[n - 1 - i] = Math.min(
                rightMin[n - 1 - i + 1],
                arr[n - 1 - i + 1]);
        }
 
        // Update original array with minimum
        // of leftMin[i] and rightMin[i]
        for (int i = 0; i < n; i++) {
            arr[i] = Math.min(leftMin[i],
                              rightMin[i]);
        }
 
        // Print the modified array.
        for (int i = 0; i < n; ++i) {
            System.out.print(arr[i] + " ");
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int arr[] = { 1, 2, 3, 2 };
        int n = arr.length;
 
        ReplaceElements(arr, n);
    }
}

Python3

# Python3 program to replace every
# element with the smallest of all
# other array elements
import sys
 
def ReplaceElements(arr, n):
 
    # There should be atleast two elements
    if (n < 2):
        print(" Invalid Input ")
        return
 
    # leftMin array stores minimum
    # element of left subarray
    leftMin = [0] * n
    leftMin[0] = sys.maxsize
 
    # rightMin array stores minimum
    # element of right subarray
    rightMin = [0] * n
    rightMin[n - 1] = sys.maxsize
 
    for i in range(1, n):
        leftMin[i] = min(leftMin[i - 1],
                             arr[i - 1])
        rightMin[n - 1 - i] = min(rightMin[n - 1 -
                                           i + 1],
                                       arr[n - 1 -
                                           i + 1])
 
    # Update original array with minimum
    # of leftMin[i] and rightMin[i]
    for i in range(n):
        arr[i] = min(leftMin[i],
                    rightMin[i])
 
    # Print the modified array.
    print(*arr, sep = " ")
 
# Driver code
arr = [ 1, 2, 3, 2 ]
n = len(arr)
 
ReplaceElements(arr, n)
 
# This code is contributed by avanitrachhadiya2155

C#

// C# program to replace every element
// with the smallest of all other
// array elements
using System;
class GFG{
 
static void ReplaceElements(int[] arr, int n)
{
     
    // There should be atleast two elements
    if (n < 2)
    {
        Console.Write(" Invalid Input ");
        return;
    }
 
    // leftMin array stores minimum
    // element of left subarray
    int[] leftMin = new int[n];
    leftMin[0] = Int32.MaxValue;
 
    // rightMin array stores minimum
    // element of right subarray
    int[] rightMin = new int[n];
    rightMin[n - 1] = Int32.MaxValue;
 
    for(int i = 1; i < n; i++)
    {
       leftMin[i] = Math.Min(leftMin[i - 1],
                                 arr[i - 1]);
       rightMin[n - 1 - i] = Math.Min(
       rightMin[n - 1 - i + 1],
            arr[n - 1 - i + 1]);
    }
 
    // Update original array with minimum
    // of leftMin[i] and rightMin[i]
    for(int i = 0; i < n; i++)
    {
       arr[i] = Math.Min(leftMin[i],
                         rightMin[i]);
    }
 
    // Print the modified array.
    for(int i = 0; i < n; ++i)
    {
       Console.Write(arr[i] + " ");
    }
}
 
// Driver code
public static void Main()
{
    int []arr = { 1, 2, 3, 2 };
    int n = arr.Length;
 
    ReplaceElements(arr, n);
}
}
 
// This code is contributed by Code_Mech

输出：

2 1 1 1

时间复杂度： O(N)
辅助空间： O(N)

另一种有效的方法：想法是通过遍历找到数组中的最小和第二个最小元素。然后，再遍历一次数组：

• 如果当前元素是最小元素，则将其替换为第二个最小元素。
• 否则用最小的元素替换当前元素

下面是上述方法的实现：

C++

// C++ program to replace every
// element with the smallest
// of all other array elements
#include 
using namespace std;
 
void ReplaceElements(int arr[], int n)
{
  
    // There should be
    // atleast two elements
    if (n < 2)
    {
        cout << " Invalid Input ";
        return;
    }
  
    // first stores minimum
    // element of the array
    int first = INT_MAX;
  
    // second stores second
    // minimum element of the array
    int second = INT_MAX;
  
    // Find the smallest and second
    // smallest elements of the array
    for(int i = 0; i < n; i++)
    {
          
       // If current element is smaller
       // than first then update both
       // first and second
       if (arr[i] < first)
       {
           second = first;
           first = arr[i];
       }
         
       // If arr[i] is in between
       // first and second
       // then update second
       else if (arr[i] < second &&
                arr[i] != first)
           second = arr[i];
    }
  
    // Update original array with
    // first and second
    for(int i = 0; i < n; i++)
    {
       arr[i] = (arr[i] == first) ?
                  second : first;
    }
  
    // Print the modified array.
    for(int i = 0; i < n; ++i)
    {
       cout << arr[i] << " ";
    }
}
  
// Driver code
int main()
{
    int arr[] = { 1, 2, 3, 2 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    ReplaceElements(arr, n);
}
  
// This code is contributed by himanshu77

Java

// Java program to replace
// every element with the smallest
// of all other array elements
 
import java.util.*;
 
class GFG {
 
    static void ReplaceElements(int[] arr, int n)
    {
 
        // There should be
        // atleast two elements
        if (n < 2) {
            System.out.println(
                " Invalid Input ");
            return;
        }
 
        // first stores minimum
        // element of the array
        int first = Integer.MAX_VALUE;
 
        // second stores second
        // minimum element of the array
        int second = Integer.MAX_VALUE;
 
        // Find the smallest and second
        // smallest elements of the array
        for (int i = 0; i < n; i++) {
 
            // If current element
            // is smaller than first
            // then update both
            // first and second
            if (arr[i] < first) {
                second = first;
                first = arr[i];
            }
 
            // If arr[i] is in between
            // first and second
            // then update second
            else if (arr[i] < second
                     && arr[i] != first)
                second = arr[i];
        }
 
        // Update original array with
        // first and second
        for (int i = 0; i < n; i++) {
 
            arr[i] = (arr[i] == first)
                         ? second
                         : first;
        }
 
        // Print the modified array.
        for (int i = 0; i < n; ++i) {
            System.out.print(arr[i] + " ");
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int arr[] = { 1, 2, 3, 2 };
        int n = arr.length;
 
        ReplaceElements(arr, n);
    }
}

Python3

# Python3 program to replace
# every element with the smallest
# of all other array elements
import sys
 
def ReplaceElements(arr, n):
     
    # There should be
    # atleast two elements
    if (n < 2):
        print(" Invalid Input ")
        return
 
    # first stores minimum
    # element of the array
    first = sys.maxsize
 
    # second stores second
    # minimum element of the array
    second = sys.maxsize
 
    # Find the smallest and second
    # smallest elements of the array
    for i in range(n):
 
        # If current element
        # is smaller than first
        # then update both
        # first and second
        if (arr[i] < first):
            second = first
            first = arr[i]
 
        # If arr[i] is in between
        # first and second
        # then update second
        elif (arr[i] < second and
              arr[i] != first):
            second = arr[i]
 
    # Update original array with
    # first and second
    for i in range(n):
        if (arr[i] == first):
            arr[i] = second
        else:
            arr[i] = first
             
    # Print the modified array.
    for i in range(n):
        print(arr[i], end = " ")
 
# Driver code
if __name__ == '__main__':
     
    arr = [ 1, 2, 3, 2 ]
    n = len(arr)
 
    ReplaceElements(arr, n)
 
# This code is contributed by Amit Katiyar

C＃

// C# program to replace every
// element with the smallest
// of all other array elements
using System;
 
class GFG{
     
static void ReplaceElements(int[] arr, int n)
{
     
    // There should be
    // atleast two elements
    if (n < 2)
    {
        Console.WriteLine(" Invalid Input ");
        return;
    }
 
    // first stores minimum
    // element of the array
    int first = Int32.MaxValue;
 
    // second stores second
    // minimum element of the array
    int second = Int32.MaxValue;
 
    // Find the smallest and second
    // smallest elements of the array
    for(int i = 0; i < n; i++)
    {
         
        // If current element
        // is smaller than first
        // then update both
        // first and second
        if (arr[i] < first)
        {
            second = first;
            first = arr[i];
        }
 
        // If arr[i] is in between
        // first and second
        // then update second
        else if (arr[i] < second &&
                 arr[i] != first)
            second = arr[i];
    }
 
    // Update original array with
    // first and second
    for(int i = 0; i < n; i++)
    {
        arr[i] = (arr[i] == first) ?
                  second : first;
    }
 
    // Print the modified array.
    for(int i = 0; i < n; ++i)
    {
        Console.Write(arr[i] + " ");
    }
}
 
// Driver code
static void Main()
{
    int[] arr = { 1, 2, 3, 2 };
    int n = arr.Length;
 
    ReplaceElements(arr, n);
}
}
 
// This code is contributed by divyeshrabadiya07

输出：

2 1 1 1

时间复杂度： O(N)
辅助空间： O(1)