JS Bin// source https://jsbin.com/gaqavizazi

Subarray_with_given_sum.js

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

var MSum = 5;
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);
  }
};