二分答案，每次貪心儘量跳遠去判斷即可

程式碼：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int N = 500005;
int L, n, m, a[N];

bool judge(int mid) {
    int s = 0;
    int cnt = 0;
    while (s != n) {
        for (int i = s + 1; i <= n + 1; i++) {
            if (a[i] - a[s] > mid) {
                if (s == i - 1) return false;
                s = i - 1;
                cnt++;
                if (cnt > m) return false;
                break;
            }
        }
    }
    return true;
}

const int INF = 0x3f3f3f3f;

int main() {
    while (~scanf("%d%d%d", &L, &n, &m)) {
        for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
        sort(a + 1, a + 1 + n);
        a[++n] = L;
        a[n + 1] = INF;
        int l = 0, r = L;
        while (l < r) {
            int mid = (l + r) / 2;
            if (judge(mid)) r = mid;
            else l = mid + 1;
        }
        printf("%d\n", l);
    }
    return 0;
}