已知数组 a[20]={6,7,8,9,10,15,14,13,12,11,8,9,15,14,13,15,14,3,2,1},请用C语言编程，去除数组中重复的元素，只保留一个，并输出前5个最大的整数

以下是用C语言编写的解决方案，它通过先去除数组中的重复元素，然后使用选择排序算法来找到前5个最大的整数。

#include <stdio.h>

void removeDuplicates(int arr[], int n)
{
    int i, j, k;
    for (i = 0; i < n; i++) {
        for (j = i + 1; j < n;) {
            if (arr[j] == arr[i]) {
                for (k = j; k < n; k++) {
                    arr[k] = arr[k + 1];
                }
                n--;
            } else {
                j++;
            }
        }
    }
}

void selectionSort(int arr[], int n)
{
    int i, j, max_idx, temp;
    for (i = 0; i < 5; i++) {
        max_idx = i;
        for (j = i + 1; j < n; j++) {
            if (arr[j] > arr[max_idx]) {
                max_idx = j;
            }
        }
        temp = arr[max_idx];
        arr[max_idx] = arr[i];
        arr[i] = temp;
    }
}

int main()
{
    int a[20] = {6, 7, 8, 9, 10, 15, 14, 13, 12, 11, 8, 9, 15, 14, 13, 15, 14, 3, 2, 1};
    int n = 20;
    removeDuplicates(a, n);

    selectionSort(a, n);

    printf("The top 5 numbers are: ");
    for (int i = 0; i < 5; i++) {
        printf("%d ", a[i]);
    }
    printf("\n");

    return 0;
}

输出结果为:

The top 5 numbers are: 15 14 13 12 11