using System;

        /*

        Given the big integer array, find the index of the first element in the continuous sequence where the sum of its elements equal to a certain number.

        Example: int[] { 2,6,4,1,8,3, ... } sum is 9, the index will be 3 for the sequence 1,8. 1 + 8 = 9.

        */

public class Program

{

    public static int FindSequenceStart(int[]array,int target){

        //o(n^2)

        for(int i=0;i<array.Length;i++){

            int sum=0;

            for(int j=i;j<array.Length;j++){

                int num=array[j];

                sum+=num;

                if(sum==target)

                    return i;

                if(sum>target)

                    break;

            }

        }

        return -1;

    }

    public static int FindSequenceStartFaster(int[]array,int target){

        int i=0;

        int j=0;

        int sum=0;

        while(i<array.Length&&j<array.Length){

            if(sum>target){

                sum-=array[i++];

            }

            else if(sum<target)

            {

                sum+=array[j++];

            }

            if(sum==target)

                return i;

        }

        return -1;

    }

    public static void Main()

    {

        Console.WriteLine(FindSequenceStart(new int[]{2,6,4,1,8,3},9));

        Console.WriteLine(FindSequenceStartFaster(new int[]{2,6,11,1,8,3},9));

    }

}