Partition to K Equal Sum - Pruning Strategies

Key optimizations: $1.$ If sum is not divisible by $k$, return false.

$2.$ Sort in descending order. Larger elements fail faster.

$3.$ If any element exceeds target sum, return false.

$4.$ Skip duplicate consecutive values to avoid redundant work.

$5.$ When $k-1$ subsets are filled, the last one is guaranteed.