Two-Sum with Hash Lookup

#include <stdio.h>

int main(void) {
    int arr[] = {2, 7, 11, 4, 5};
    int n = (int)(sizeof(arr) / sizeof(arr[0]));
    int target = 9;
    int seen_value[5];
    int seen_index[5];
    int seen_count = 0;
    int first = -1;
    int second = -1;
    for (int i = 0; i < n; ++i) {
        int need = target - arr[i];
        for (int j = 0; j < seen_count; ++j) {
            if (seen_value[j] == need) {
                first = seen_index[j];
                second = i;
                break;
            }
        }
        if (first != -1) {
            break;
        }
        seen_value[seen_count] = arr[i];
        seen_index[seen_count] = i;
        seen_count++;
    }
    printf("[%d, %d]\n", first, second);
    return 0;
}