如何交换数组中的最后一个元素和最大元素？

Question

How to swap the maximum and last element of an array?

I want to write the program which requests natural number NN (no more than 100), further sequence from NN of various numbers, changes places of the last element and the maximum, leaving other elements without change, and deduces the received array.

Sample Input 1:

8
3 6 12 1 7 19 25 4

Sample Output 1:

3 6 12 1 7 19 4 25

---

This is what I tried:

#include <iostream>
using namespace std;
int main() 
{
    int i,arr[100],n;
    cin>>n;
    int imin=0;
    for (int i=0; i<n; i++){cin>>arr[i];}

    int max=0;
    for (i=1;i<n;i++) 
    {
        if (arr[i]>arr[max])
            max=i;
        int tmp=arr[max];
        arr[max]=arr[n-1];
        arr[n-1]=tmp;
        for (i=0;i<n;i++)
            cout <<arr[i]<< " ";
        cout << "\n";  
    }  
    return 0;
}

It does not change places the maximum and the last. How can I do this?

Answer 1

I recommend using a loop to find the index of the maximum value, then outside of the loop swap the values .

int index = 0;
int max_value = arr[0];
int index_of_max_value = 0;
for (index = 1; index < n; ++n)
{
    if (arr[index] > max_value)
    {
        max_value = arr[index];
        index_of_max_value = index;
    }
}
std::swap(arr[index_of_max_value], arr[n-1]);

Answer 2

#include <algorithm> // max_element, iter_swap

// ...

    auto me = std::max_element(arr, arr + n); // get an iterator to the largest element
    std::iter_swap(me, arr + n - 1); // swap the value at "me" with the last element

Answer 3

To swap the last element of the array with the maximum element of the array, first you need to find the index of the maximum element by traversing the full array. Then swap the last index of the array with the index that you get for maximum element. Your code had some mistakes i fixed them, have a look. Also see the indentation that i did, it is a good practice and it makes the code more redable.

swap(x, y) is a builtin function to swap two variable values.

You can do this like:

#include <iostream>
using namespace std;
int main() 
{
    int n;

    cin>>n;
    
    //int arr[n]; 
    // as said in the comment it's not the standard way to declare variable length array in C++, either use fixed length or use vector in c++

    vector<int> arr(n + 1);

    for (int i = 0; i < n; i++) cin >> arr[i];

    int mx = 0, idx;

    for(int i = 0; i < n; i++){
        if(arr[i] > mx){
            mx = arr[i];
            idx = i;
        }
    }

    swap(arr[n-1], arr[idx]); // swap is a builtin function
   
    for(int i = 0; i < n; i++)
         cout << arr[i] << " ";
    cout << "\n";  
 }  
return 0;}

Answer 4

First, you have to find the largest element index. Then swap it with the last element. Some cases may occur that the last element is the largest element so the array doesn't change at all or there are multiple maximum elements so you have to decide what to do next which element you want to swap, the first maximum element or the other one with the last element of the array.

#include<iostream>
#include<vector>
using namespace std;
int main()
{
    int n;
    cin >> n;
    vector<int> arr(n + 1);
    for(int i = 0; i < n; i++){
        cin >> arr[i];
    }

    int maxi = 0;
    for(int i = 0; i < n; i++){
        if(arr[i] > arr[maxi])
            maxi = i;
    }
    // swap is a builtin function that interchange two elements
    swap(arr[maxi], arr[n - 1]); 
    for(int i = 0; i < n; i++)
        cout << arr[i] << " ";
    cout << "\n";
    return 0;
}

Sample Input:

8
3 6 12 1 7 19 25 4
4
1 2 3 4

Sample Output:

3 6 12 1 7 19 4 25
1 2 3 4

Answer 5

#include <iostream>
using namespace std;
int main() 
    {
    int i,arr[100],n;
    cin>>n;
    int imin=0;
    for (int i=0; i<n; i++){cin>>arr[i];}

    int max=0;
    for (i=1;i<n;i++) 
    {
        if (arr[i]>arr[max])
            max=i;
    } // closed the for loop here//

    int tmp=arr[max];
    arr[max]=arr[n-1];
    arr[n-1]=tmp;
    for (i=0;i<n;i++)
         cout <<arr[i]<< " ";
     cout << "\n";  
 
     return 0;
    }

Your code is good just needed to close the for loop after the max=i statement. If you have any other issue then ask.