二分搜索 POJ 3258 River Hopscotch

题目传送门

 /*
     二分：搜索距离，判断时距离小于d的石头拿掉
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 using namespace std;

 typedef long long ll;
 const int MAXN = 5e4 + ;
 const int INF = 0x3f3f3f3f;
 ll a[MAXN];
 int n, m;

 bool check(ll d)    {
     int last = ;  int cnt = ;
     for (int i=; i<=n+; ++i)  {
         if (a[i] - a[last] <= d)    cnt++;
         else    last = i;
     }
     return cnt > m;
 }

 int main(void)  {       //POJ 3258 River Hopscotch
     //freopen ("POJ_3258.in", "r", stdin);

     ll x;
     while (scanf ("%I64d%d%d", &x, &n, &m) == )    {
         a[] = ;   a[n+] = x;
         for (int i=; i<=n; ++i)    {
             scanf ("%I64d", &a[i]);
         }

         sort (a, a+n+);    ll l = , r = a[n+];
         while (l <= r)   {
             ll mid = (l + r) >> ;
             if (check (mid))    r = mid - ;
             else    l = mid + ;
         }
         printf ("%I64d\n", l);
     }

     return ;
 }