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FLATLAND-SPACE-STATIONS Solution

/*
*  Author: Arpit Bhayani
*  https://arpitbhayani.me
*/
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <climits>
#include <deque>
#include <iostream>
#include <list>
#include <limits>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>

#define ll long long

#define MIN(a, b) a < b ? a : b
#define MAX(a, b) a > b ? a : b

using namespace std;

int i = 0;
char ch;
while((ch = getchar()) != '\n') {
str[i++] = ch;
}
str[i] = '\0';
return i;
}

int compar(const void * a, const void * b) {
return *((int *)a) > *((int *)b);
}

int main(int argc, char *argv[]) {
int n, k;
scanf("%d%d", &n, &k);

int * arr = (int *) calloc(k, sizeof(int));

for(int i = 0 ; i < n ; i++) {
scanf("%d", &arr[i]);
}

if(k == n) {
printf("0\n");
}
else {
qsort(arr, k, sizeof(int), compar);
int ans = INT_MIN;
for(int i = 0 ; i < (k - 1) ; i++) {
int res = 0;
if(arr[i+1] - arr[i] == 1) {
res = 0;
}
else {
res = (arr[i+1] - arr[i]) / 2;
}
ans = MAX(ans, res);
}

ans = MAX(ans, arr);
ans = MAX(ans, n - 1 - arr[k-1]);

printf("%d\n", ans);
}
free(arr);

return 0;
}