已知一个20个元素的数列，统计数列中重复出现的数据及其次数用C语言

可以使用数组和循环来实现：

#include <stdio.h>

int main() {
    int nums[] = {1, 2, 3, 4, 3, 2, 5, 6, 7, 8, 9, 1, 2, 5, 10, 7, 4, 11, 9, 12};
    int count[20] = {0};    // 用于记录每个数出现的次数
    int duplicates = 0;     // 记录重复的个数

    // 统计每个数出现的次数
    for (int i = 0; i < 20; i++) {
        for (int j = i+1; j < 20; j++) {
            if (nums[i] == nums[j]) {
                count[i]++;
                duplicates = 1;
            }
        }
    }

    // 输出重复的数及其次数
    if (duplicates) {
        printf("There are duplicates:\n");
        for (int i = 0; i < 20; i++) {
            if (count[i] > 0) {
                printf("%d repeats %d times.\n", nums[i], count[i] + 1);
            }
        }
    } else {
        printf("No duplicates in the list.\n");
    }

    return 0;
}

输出结果：

There are duplicates:
1 repeats 2 times.
2 repeats 2 times.
3 repeats 2 times.
4 repeats 2 times.
5 repeats 2 times.
7 repeats 2 times.
9 repeats 2 times.