90分卡了5天，大佬帮帮我

#include <bits/stdc++.h>
#define int long long
using namespace std;
int l,n,m,a[10000001];
bool check(int x){
    int t=0,num=0;
    for(int i=1;i<=n;i++)
        if(a[i]-t<x) num++;
        else t=a[i];
    if(l-t<x) num++;
    return num<=m;
}
signed main(){
    cin >> l >> n >> m;
    for(int i=1;i<=n;i++) cin >> a[i];
    int ll=0,rr=l,mid;
    while(ll+1<rr){
        mid=(ll+rr)/2;
        if(check(mid)) ll=mid;
        else rr=mid;
    }
    cout << ll;
    return 0;
}

        ___
       |   |
       |   |
   ____|  _|_______
__/      |         |
         |_________|_
     |   |           |
     |   |___________|
   __/   |           |
         |___________|
___       |        |
   \______|________|