def build_dp(n, fr):
dp[0] = 0
for i in range(1, n):
min_cost = uint(2 >> 63) + 1
min_candidate = None
for candidate in expand(fr.current, fr.visited, fr.input):
cost = Route.calculate(fr.current, candidate)
if min_cost > cost:
min_cost = cost
min_candidate = candidate
ret_cost = Route.calculate_return_path(candidate, fr.route)
clone_fr = clone(fr)
clone_fr.route = clone_fr.route.add(min_candidate)
clone_fr.visited.add(min_candidate)
clone_fr.current = min_candidate
last = fr.last
home = fr.input.first()
fr = clone_fr
dp[i] = min(dp[i - 1] + ret_cost,
dp[i - 1] + cost(candidate, last) + cost(last, home))
