[NOIP 2015] 跳石头

[题目链接]

          http://uoj.ac/problem/148

[算法]

         二分答案，时间复杂度O(NlogL)

[代码]

        

#include<bits/stdc++.h>
using namespace std;
#define MAXN 50010
typedef long long ll;

ll i,L,N,M,l,r,mid,ans;
ll dis[MAXN];

template <typename T> inline void read(T &x)
{
        ll f = 1; x = 0;
        char c = getchar();
        for (; !isdigit(c); c = getchar())
        {
                if (c == '-') f = -f;
        }
        for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - '0';
        x *= f;
}
inline bool check(ll d)
{
        ll i,c = 0,cnt = 0;
        bool flag = false;
        for (i = 1; i <= N; i++)
        {
                if (dis[i] - dis[c] >= d) c = i;        
                else cnt++;
                if (cnt > M) return false;
        }
        if (L - dis[c] < d) cnt++;
        if (cnt <= M) return true;
        return false;
}

int main() 
{
        
        read(L); read(N); read(M);
        dis[0] = 0;
        for (i = 1; i <= N; i++) read(dis[i]);
        l = 1; r = 1e15;
        while (l <= r)
        {
                mid = (l + r) >> 1;
                if (check(mid))
                {
                        l = mid + 1;
                        ans = mid; 
                } else r = mid - 1;
        }
        printf("%lld\n",ans);
        
        return 0;
    
}