Question

How to find K most frequent elements in an unsorted array with C

Answer 1

#include <stdio.h>
#include <stdlib.h>

#define MAX_NUMBER_SIZE 50 + 1

int CompareDescending(const void* a, const void* b) {
    return (*(int*)b - *(int*)a);
}

void PrintKMostFrequentNumbers(int arr[], int len, int K) {
    int frequency[MAX_NUMBER_SIZE] = { 0 };
    int equivalent_number[MAX_NUMBER_SIZE] = { 0 };

    for (int i = 0; i < len; i++) {
        frequency[arr[i]]++;
    }

    for (int i = 0; i < MAX_NUMBER_SIZE; i++) {
        equivalent_number[frequency[i]] = i;
    }

    qsort(frequency, MAX_NUMBER_SIZE, sizeof(int), CompareDescending);

    for (int i = 0; i < K; i++) {
        printf("%d ", equivalent_number[frequency[i]]);
    }
}

int main()
{
    // up to 50, at this time 
    int arr[] = { 4, 5, 19, 30, 7, 19, 8, 19, 3, 5, 6, 19, 27, 19, 3, 5, 5 }; 
    int len = sizeof(arr) / sizeof(arr[0]);
    int K = 2;

    PrintKMostFrequentNumbers(arr, len, K);

    return 0;
}





/*
run:

19 5

*/

 

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