/COMPUTER SCIENCE 161.01
//WEDNESDAY NOV 8TH 2017

//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.

lastNames = new Array("Carrigan", "Cronk", "Donelson", "Furrow",
		      "Haynes", "King", "Lemon", "Lowman",
                      "Quinn", "Reilly", "Shaw", "Sinsel",
                      "Smith", "Tribble", "Weinberg");

firstNames  = new Array("Riley", "Kyle", "Andrew", "Jake",
                       "Seth", "David", "Charlie", "Miles",
			"Donovan", "Andrew", "Connor", "Jacob",
                        "Brandon", "Preston", "Brendan");

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"