题解 100% AC

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