uoj #148. 【NOIP2015】跳石头 二分

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <queue>
#include <stack>
#include <bitset>
using namespace std;
#define pb(x) push_back(x)
#define ll long long
#define mk(x, y) make_pair(x, y)
#define lson l, m, rt<<1
#define mem(a) memset(a, 0, sizeof(a))
#define rson m+1, r, rt<<1|1
#define mem1(a) memset(a, -1, sizeof(a))
#define mem2(a) memset(a, 0x3f, sizeof(a))
#define rep(i, n, a) for(int i = a; i<n; i++)
#define fi first
#define se second
typedef pair<int, int> pll;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int mod = 1e9+7;
const int inf = 1061109567;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
int a[50006], n, m;
int check(int x) {
    int pre = 0, sum = 0;
    for(int i = 1; i<=n; i++) {
        if(a[i]-pre<x) {
            sum++;
        } else {
            pre = a[i];
        }
    }
    return sum<=m;
}
int main()
{
    int L;
    cin>>L>>n>>m;
    for(int i = 1; i<=n; i++) {
        scanf("%d", &a[i]);
    }
    a[++n] = L;
    ll l = 0, r = L, ans = r;
    while(l<=r) {
        int mid = (l+r)>>1LL;
        if(check(mid)) {
            l = mid+1;
            ans = mid;
        } else {
            r = mid-1;
        }
    }
    cout<<ans<<endl;
    return 0;
}