longest.c

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

#define MAX 105

void sort(int *array, int k) {
  int* ord = (int*)malloc(k * sizeof(int));

  int i = 0;
  
  int largest = array[0];
  for(i = 1; i < k; i++) {
    if(array[i] > largest)
      largest = array[i];
  }

  int* aux = (int*)malloc(largest * sizeof(int));

  for(i = 0; i <= largest; i++)
    aux[i] = 0;
  
  for(i = 0; i < k; i++)
    aux[array[i]]++;
  
  for(i = 1; i <= largest; i++)
    aux[i] += aux[i - 1];
  
  for(i = k - 1; i >= 0; i--) {
    ord[aux[array[i]] - 1] = array[i];
    aux[array[i]]--;
  }
  
  for(i = 0; i < k; i++)
    array[i] = ord[i]; 
}

int longest_sequence(int* array, int k) {
  sort(array, k);
  
  int i = 0, sequence = 0, maxsequence = 0;

  for(i = 0; i < k - 1; i++) {
    int test_next = array[i] + 1;
    if(array[i + 1] == test_next)
      sequence++;
    else
      sequence = 0;

    if(sequence > maxsequence)
      maxsequence = sequence; 
  }

  return maxsequence + 1;
}

int main() {
  int* nums = (int*)malloc(sizeof(int) * MAX);
  int n, i;

  scanf("%d", &n);
  
  if(n > MAX) return -1;

  for(i = 0; i < n; i++) {
    scanf("%d", &nums[i]);
    if(nums[i] > 109 || nums[i] < -109) return -1;
  }

  printf("%d\n", longest_sequence(nums, n));
  return 0;
}