Javascript Question
Javascript Recursion?
I am practicing recursion. Conceptually I understand how this should work, (see below) but my code isn't working.
Please tell me what I am doing wrong., and please please explain each step why your code works. Clear Explanation is ten times better than just giving me a code that works.
/*
buildList(0, 5) == buildList(0, 5 - 1) // [0]
buildList(0, 4) == buildList(0, 4 - 1) // [0,0]
buildList(0, 3) == buildList(0, 3 - 1) // [0,0,0]
buildList(0, 2) == buildList(0, 2 - 1) // [0,0,0,0]
buildList(0, 1) == buildList(0, 1 - 1) // [0,0,0,0,0]
*/
var buildList = function(value, length) {
var result = [];
if (length === 0) {
return result;
}
result.push(value);
return buildList(result.push(value), length - 1);
};
buildList(0, 5);
I understand how the recursion works on conceptual level.
Answer Source
Your approach can't work, because the base case returns a new empty array, and other cases return the result of the recursion.
Instead, you should first recurse and then push
var buildList = function(value, length) {
if (length <= 0) return [];
var recur = buildList(value, length-1);
recur.push(value);
return recur;
};
Alternatively, in the base case you can avoid creating a new array
var buildList = function(value, length, array=[]) {
if (length <= 0) return array;
array.push(value);
return buildList(value, length-1, array);
};