Reputation: 125
I have two arrays where I need to compare values and get the duplicates. I wrote most of the code but seem to be stumped on the comparison.
Here is my code:
function compare(arr1, arr2) {
for (var i = 0; i< arr1.length; i++) {
for (var j = 0; j < arr2.length; j++) {
if (arr1[i] == arr2[j]) {
console.log[i];
}
}
}
}
compare([5, 3, 2, 5, 1, 6], [6, 4, 2, 7, 10]);
I get the for loops to print all of the numbers, but for some reason the if statement comparison doesn't work. Is there something I am not getting about comparing values in arrays?
I am not looking for a straight up answer but guidance if possible.
Upvotes: 0
Views: 116
Reputation: 215059
Your code is quadratic in time since it iterates the second array for each item in the first array. A linear time solution is to convert the first array into a hash table, and then, for each item in the second one, instantly check if it is in the hash.
function intersect(a, b) {
var hash = {};
a.forEach(function(x) { hash[x] = 1 });
return b.filter(function(x) { return hash[x] === 1 });
}
c = intersect([5, 3, 2, 5, 1, 6], [6, 4, 2, 7, 10]);
document.write(c)
Do note, however, that this only works if items to compare are primitives, you cannot put objects in a hash, so the code has to be quadratic:
function intersect(a, b) {
return a.filter(function(x) {
return b.indexOf(x) >= 0
});
}
a = {x:'a'};
b = {x:'b'};
c = {x:'c'};
d = {x:'d'};
i = intersect([a,b,c], [a,b,d]);
document.write(JSON.stringify(i));
Regarding your bit about improving your current code, I suggest that you make your javascript more idiomatic, in particular,
for
loops==
Upvotes: 2