NOIP2015 TG D2T1 stone

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
int l, n, m, d[50005];
bool check(int value)
{
int now = 0, ans = 0;

for(int i = 1; i <= n; i++)
if(d[i] - now >= value)
{
ans++;
now = d[i];
}

if(l - now < value) ans--;

if(ans >= n - m) return 1;
else return 0;
}

int main()
{
freopen("stone.in", "r", stdin);
freopen("stone.out", "w", stdout);

scanf("%d%d%d", &l, &n, &m);

for(int i = 1; i <= n; i++) scanf("%d", &d[i]);

int ll = 0, r = l + 1;

while(ll < r)
{
int mid = (ll + r) / 2 + 1;

if(check(mid)) ll = mid;
else r = mid - 1;
}

printf("%d", ll);
}