Subset Sum - Key Observation

Each integer from $0$ to $2^n - 1$ represents exactly one subset. The mask tells you which elements to include. Iterate through all masks, and for each one, compute the sum of included elements. For mask $= 5$ (binary $101$) with array $[3, 1, 4]$: bits $0$ and $2$ are set, so include $arr[0] = 3$ and $arr[2] = 4$. Sum $= 7$.

This is brute-force, but $2^{20}$ operations is fast enough. No clever DP (dynamic programming) needed here. The bitmask just gives you a clean way to enumerate all subsets without recursion.