it's like sum of combinations.. nC0 + nC1 + nC2 ... +nCk +..nCn = 2^n;

where "k" is the number of lights at a moment of time. we'll traverse from [0 , n-1] and creating 2^n slowly with limit 1e5

at last we won't consider the case where no light bulb is ON.

2^n - nC0 -> 2^n - 1

let l = 100000;

function lights(n: number): number {
    // Write your code here
    let tot = 1;
    for(let i = 0; i<n; i++){
        tot *= 2;
        tot = tot%l
    }
    return tot-1;
*  }