Infinite recursion in combinationSum

[dubzzz]

Details:

combinationSum fails with Maximum call stack size exceeded.
It seems that there is an infinite recursion in it.

Step to reproduce: combinationSum([0], 1)

Bug 1: presence of 0 produces an infinite loop
Bug 2: presence of small entries compared to target produces a stack size exceeded - combinationSum([1], 100000)

Fix

I can issue a PR with the fix.

How did I find it?

Thanks to property based testing framework fast-check.
The property was the following:

import fc from 'fast-check';

fc.assert(
    fc.property(
        fc.set(fc.nat()),
        fc.nat(),
        (elements, target) => {
            const combinations = combinationSum(elements, target);
            const combinationsStr = combinations.map(arr => arr.join(','));
            // no duplicates
            expect([...new Set(combinationsStr)]).toEqual(combinationsStr);
            // right sum
            for (const comb of combinations)
                expect(comb.reduce((a,b) => a+b, 0)).toBe(target);
        }
    )
)

Or:

for any elements - array of unique positive integers, target - positive integer
the output of combinationSum(elements, target) does not contain any duplicates
and all its entries sum to target