//COMPUTER SCIENCE 161.01
//WEDNESDAY NOV 13th 2013

//BINARY SEARCH

//THE PROGRAM BELOW PERFORMS THE BINARY SEARCH ALGORITHM
//IT IS MUCH MORE EFFICIENT THAN SEQUENTIAL SEARCH
//BUT IT REQUIRES THAT THE lastNames ARRAY BE IN ALPHABETICAL ORDER

//HERE, N is 15.

firstNames  = new Array("Charles", "Jeffrey", "Daniel", "Marcus", "George", "Bryce", "John", "Paul",
                        "Tanner", "Ringo", "Stephen", "Tyler", "Christian", "Marcus", "Michael");

lastNames   = new Array("Barham", "Decker", "Fogleman", "Goodman", "Harrison", "Jones", "Lennon", "McCartney",
                        "Mullins", "Starr", "Vassor", "Walton", "Wilder", "Williams", "Willis");


N = lastNames.length;
desired = prompt("Enter last name of desired person: ");

first = 0;  
last = N-1;
found = false;

count = 0;  //to count loop iterations

while (first <= last && found == false) {

      mid = (first + last)/2;     

      alert("first = " + first + "  last = " + last + "  mid = " + mid);

      if (desired > lastNames[mid])
           first = mid + 1;
      else if (desired < lastNames[mid])
           last = mid - 1;
      else
           found = true; 

count++;
}

 
if (found == true)
  alert("Happy Wednesday to " + firstNames[mid]);
else {
  alert("first = " + first + "  last = " + last);
  alert("Could not find " + desired);
}

 
//REPORT AT BOTTOM… 

count + " comparisons"