Why is my algorithm returning “-1” meaning that target value 73 isn’t in the array? (When clearly 73 is in the array). [this is from Khan Academy, but isn't helping]
It's supposed to return 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(max >= min) {
guess = floor((max*1 + min*1) / 2);
if (guess === targetValue) {
return guess;
} else if (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, 73);
println("Found prime at index " + result);
Your function doSearch()
doesn't compare any value of the array
to the targetValue
. You need to access the guess
position and compare it, like this:
var doSearch = function(array, targetValue) {
var min = 0;
var max = array.length - 1;
var guess;
while(max >= min){
guess = Math.floor((max*1 + min*1) / 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, 73);
console.log("Found prime at index " + result);
Warning: The function
floor()
doesn't exist in JavaScript. You should useMath.floor()
. Also, the functionprintln()
. Useconsole.log()
instead.