TSP - Implementation

Here's the full solution:

function tsp(cost, n)
    INF := large number
    dp := 2D (two-dimensional) array [2^n][n], filled with INF
    dp[1][0] := 0
    // start at city 0
    for mask := 1 to 2^n - 1
        for last := 0 to n - 1
            if dp[mask][last] = INF then
                continue
            if (mask >> last) & 1 = 0 then
                continue
            for next := 0 to n - 1
                if (mask >> next) & 1 = 1 then
                    continue
                newMask := mask | (1 << next)
                dp[newMask][next] := min(dp[newMask][next], dp[mask][last] + cost[last][next])
    ans := INF
    for last := 0 to n - 1
        ans := min(ans, dp[2^n - 1][last] + cost[last][0])
    return ans if ans < INF else "IMPOSSIBLE"

Time: $O(n^2 \cdot 2^n)$. Space: $O(n \cdot 2^n)$. For $n = 20$, this runs in a few seconds.

Time: $O(n^2 \cdot 2^n)$. Space: $O(n \cdot 2^n)$.