C++ Practice Questions – Sorting Problem (2)

Time Limit: 2s Memory Limit: 192MB

Problem Description

Sort ten numbers in descending order

Input Format

Ten integers

Output Format

Output these ten numbers in descending order

Sample Input

1 2 3 4 5 6 7 8 9 10

Sample Output

10 9 8 7 6 5 4 3 2 1

Code

#include <iostream>#include <algorithm> // For sort function#include <functional> // For greater<int>()using namespace std;
int main() {    int arr[10];
    // Input ten integers    for (int i = 0; i < 10; i++) {        cin >> arr[i];    }
    // Use sort function for descending order sorting    sort(arr, arr + 10, greater<int>());
    // Output sorted result    for (int i = 0; i < 10; i++) {        cout << arr[i];        if (i < 9) cout << " "; // No space after the last number    }    cout << endl;
    return 0;}

Output Result

Code Explanation: (1) Header Files: a) <iostream> for input and output b) <algorithm> includes the sort function c) <functional> includes greater<int>() for descending order sorting (2) Array Storage: a) Use an integer array arr of size 10 to store the ten input numbers (3) Input Handling: a) Use a for loop to read 10 integers into the array (4) Descending Order Sorting: a) sort(arr, arr + 10, greater<int>()) sorts the array in descending order b) greater<int>() is a function object that tells the sort function to arrange in descending order (5) Output: a) Use a for loop to output the sorted array elements b) Add spaces between numbers, no space after the last number

Another Implementation Method (Sort Ascending then Reverse):

#include <iostream>#include <algorithm>using namespace std;
int main() {    int arr[10];
    for (int i = 0; i < 10; i++) {        cin >> arr[i];    }
    // First sort in ascending order    sort(arr, arr + 10);
    // Then reverse the array to get descending order    reverse(arr, arr + 10);
    for (int i = 0; i < 10; i++) {        cout << arr[i] << " ";    }    cout << endl;
    return 0;}

Third Method (Manual Comparison and Swap):

#include <iostream>using namespace std;
int main() {    int arr[10];
    // Input    for (int i = 0; i < 10; i++) {        cin >> arr[i];    }
    // Use selection sort for descending order    for (int i = 0; i < 9; i++) {        for (int j = i + 1; j < 10; j++) {            if (arr[i] < arr[j]) { // If the previous number is less than the next number, swap                int temp = arr[i];                arr[i] = arr[j];                arr[j] = temp;            }        }    }
    // Output    for (int i = 0; i < 10; i++) {        cout << arr[i] << " ";    }    cout << endl;
    return 0;}

Extended Knowledge:Three Uses of the sort Function:

1. Ascending: sort(arr, arr+10) or sort(arr, arr+10, less<int>())
2. Descending: sort(arr, arr+10, greater<int>())
3. Custom sorting rules

Sorting Algorithm Comparison:

• sort() function: Efficient, O(n log n) time complexity
• Selection sort: O(n²) time complexity, suitable for understanding algorithm principles
• In practical programming, it is recommended to use the sort() function for efficiency and simplicity

Teaching Suggestions:

• For beginners, it is recommended to use the first method (sort + greater)
• The second method can help understand the concept of array reversal
• The third method is suitable for explaining the basic principles of sorting algorithms

C++ Basic Tutorial Collection

C++ Basic Materials

1. C++ Output

2. C++ Variables

3. C++ Input

4. C++ Expressions

5. IF Statements

6. IF Applications

7. WHILE Loop Statements

8. FOR Loop Statements

9. Arrays

10. One-Dimensional Arrays

11. Two-Dimensional Arrays

12. C++ Functions

13. C++ File Operations – Writing Files

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