Given an integer array `nums` and an integer `k`, return `true` if it is possible to divide all elements into `k` non-empty subsets whose sums are all equal.
Example 1
Input:nums = [4,3,2,3,5,2,1], k = 4
Output:true
Explanation:Subsets (5),(1,4),(2,3),(2,3) each sum to 5.