I was following the pseudo code to implement algorithm on the link but don't know what's wrong with my code.
Here is my code :
/* Returns either the index of the location in the array,
or -1 if the array did not contain the targetValue */
var doSearch = function(array, targetValue) {
var min = 0;
var max = array.length - 1;
var guess;
while(min < max) {
guess = (max + min) / 2;
if (array[guess] === targetValue) {
return guess;
}
else if (array[guess] < targetValue) {
min = guess + 1;
}
else {
max = guess - 1;
}
}
return -1;
};
var primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37,
41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97];
var result = doSearch(primes, 2);
println("Found prime at index " + result);
//Program.assertEqual(doSearch(primes, 73), 20);
To get a value from an array you need to specify a whole number like array[1]
. array[1.25]
will return undefined
in your case.
To get it working I simply added Math.floor
inside you loop to insure we get a whole number.
EDIT: As @KarelG pointet out you also need to add <=
in your while loop. This is for situations where min
and max
have become the same, in which case guess === max === min
. Without the <=
the loop would not run in these situations and the function would return -1
.
function (array, targetValue) {
var min = 0;
var max = array.length - 1;
var guess;
while(min <= max) {
guess = Math.floor((max + min) / 2);
if (array[guess] === targetValue) {
return guess;
}
else if (array[guess] < targetValue) {
min = guess + 1;
}
else {
max = guess - 1;
}
}
return -1;
}
You could use either of Math.floor
, Math.ceil
, and Math.round
.
I hope this was a small help, I am not very good at explaining, but I'll do my be to elaborate.