Energy Charger

#include<stdio.h>
typedef long long int ll;
int main()
{
    int n,T;
    scanf("%d %d",&n,&T);
    ll arr[n];
    ll L = 1; //max elem
    ll R = 0; //sum elem
    for(int i = 0 ; i < n ; i ++){
        scanf("%lld",&arr[i]);
        if(arr[i] > L)L = arr[i];
        R += arr[i];
    }
    if(T == 1){
        printf("-1");
        return 0;
    }
    ll aL=L-1,aR=R+1;

    ll l = L , r = R;
    while(l <= r){
        ll m = (l+r)/2;

        ll EnergyNow = 0;
        ll TotalCharge = 0;
        for(int i = 0 ; i < n ; i ++){
            if(EnergyNow >= arr[i]){
                EnergyNow -= arr[i];
            }else{
                EnergyNow = m - arr[i];
                TotalCharge++;
            }
            if(TotalCharge > T){
                break;
            }
        }
        if(TotalCharge <= T){
            if(TotalCharge == T){
                aL = m;
            }
            r = m - 1;
        }else{
            l = m + 1;
        }
    }
    l = L ; r = R;
    while(l <= r){
        ll m = (l+r)/2;

        ll EnergyNow = 0;
        ll TotalCharge = 0;
        for(int i = 0 ; i < n ; i ++){
            if(EnergyNow >= arr[i]){
                EnergyNow -= arr[i];
            }else{
                EnergyNow = m - arr[i];
                TotalCharge++;
            }
            if(TotalCharge > T){
                break;
            }
        }
        if(TotalCharge >= T){
            if(TotalCharge == T){
                aR = m;
            }
            l = m + 1;
        }else{
            r = m - 1;
        }
    }
//  printf("%lld",(aR-aL+1 == ((L-1) - (R+1) + 1) ? -1 : aR-aL+1));
    printf("%lld",aR-aL+1);
    return 0;
}