Partition into two equal subsets – Algorithmic problem solving in Typescript

My solution to a “Daily Coding Problem” that I received in my mail today.

Given a multiset of integers, return whether it can be partitioned into two subsets whose sums are the same.

For example, given the multiset {15, 5, 20, 10, 35, 15, 10}, it would return true, since we can split it up into {15, 5, 10, 15, 10} and {20, 35}, which both add up to 55.

Given the multiset {15, 5, 20, 10, 35}, it would return false, since we can’t split it up into two subsets that add up to the same sum.

Here’s my solution in Typescript,

sixty(arr: number[]): boolean {
    if(arr == null) {
        return false;
    }
    //step 1: check if the sum is odd?
    const reducer = (v1: number, v2: number) => v1 + v2;
    let total = arr.reduce(reducer);
    if(total % 2 != 0) {
        //if so then it's impossible to find 2 'equal' partitions
        return false;
    }
    var returnVal = true;
    let half = total / 2;
    //get half and then find 2 subsets that total upto that no
    return this.hasSubset(arr, arr.length, total / 2);
}
private hasSubset(arr: number[], idx: number, sum: number): boolean {
    if(sum == 0) {
        return true;
    } else if(idx == 0 && sum != 0) {
        return false;
    }
    if(arr[idx - 1] > sum) {
        return this.hasSubset(arr, idx - 1, sum);
    } 
    return this.hasSubset(arr, idx - 1, sum)
    || this.hasSubset(arr, idx -1 , sum - arr[idx -1] );
}

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