var dataStructure = { "head": -1, "Sum":0, "Sequence": [] };

​

// var MSum = 12;

// var seq  = [1,2,3,7,5];

​

var MSum = 15;

var seq = [1,2,3,4,5,6,7,8,9,10];

​

​

var outcome = "-1";

​

for(var i = 0; i < seq.length; i++){

//   console.log(i+ " " +dataStructure.head+" - "+dataStructure.Sum);

  if(dataStructure.Sum < MSum) {

    dataStructure.Sequence.push(seq[i]);

    dataStructure.Sum += seq[i];    

  }

  if (dataStructure.Sum > MSum){

    var temp = dataStructure.Sequence.shift();

    dataStructure.Sum -= temp;

    dataStructure.head += 1;

  }

  if (dataStructure.Sum == MSum){

    dataStructure.head += 2;

    console.log(dataStructure.head +" "+(i+1));

    break;

  }

  if ( i == seq.length-1){

    console.log(-1);

  }

};

​