/COMPUTER SCIENCE 161.01
//WEDNESDAY NOV 13TH 2019

//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("Dawson", "Eisele", "Flanagan", "Gaither", "Harrison", 
                       "Lennon", "Lively", 
                       "McCartney",
                       "Puhlick", "Purdie", "Saenz", "Starr", "Turner",  
                       "Valente", "White");


firstNames  = new Array("Ben", "Jackson", "Will", "James", "George",
              "Paul",
              "Peyton", "Boyce", "Manuel", "Ringo", "Chase",
              "Tom", "Jonathan");


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"