//COMPUTER SCIENCE 161.01
//MONDAY APRIL 8TH

//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("Devin", "Paul", "Derek", "Kyle", "Hunter", "Elijah", "Loren", "Brian",
                        "Tanner", "Tyler", "Cody", "Tyler", "Charles", "Alex", "Aaron");

lastNames   = new Array("Baker",  "Boydoh", "Fimian", "Fraser", "Guttendorf", "Hawkins", "Hubbard", "Hulsizer", 
                        "Iglio", "Johnson", "Joyner",  "Lange", "MacSherry",  "Smith", "Van Allen");


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 Monday to " + firstNames[mid]);
else {
  alert("first = " + first + "  last = " + last);
  alert("Could not find " + desired);
}

 
//REPORT AT BOTTOM… 

count + " comparisons"