题解在此

#include <iostream>
using namespace std;
int L,n,m;
int a[50010];
bool check(int x){
    int sum=0;
    for (int i=0;i<=n;i++){
        int j=i;
        while (j<=n+1&&a[j]-a[i]<x){
            j++;
        }
        sum+=j-i-1;
        i=j-1;
    }
    return sum<=m;
}
int main(){
    cin>>L>>n>>m;
    for (int i=1;i<=n;i++){
        cin>>a[i];
    }
    a[n+1]=L;
    int l=1,r=L;
    int ans=0;
    while (l<=r){
        int mid=(l+r)/2;
        if (check(mid)){
            ans=mid;
            l=mid+1;
        }else{
            r=mid-1;
        }
    }
    cout<<ans;
    return 0;
}