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# Branch and Bound Algorithm Technique

Branch and bound is another algorithm technique that we are going to present in our multi-part article series covering algorithm design patterns and techniques. B&B, as it is often abbreviated, is one of the most complex techniques and surely cannot be discussed in its entirety in a single article. Thus, we are going to focus on the so-called A* algorithm that is the most distinctive B&B graph search algorithm.

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October 21, 2008

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Branch and Bound Algorithm Technique - Conclusions of the Knapsack
(Page 4 of 4 )

The Knapsack problem is a combinatorial optimization problem. You are given a set of items, each with its own cost and value, and you are to determine the number of each item that you should pack into the knapsack so that the total cost doesn't exceed the given limitation, but the total value is as high as possible. As you can see, this is a maximization problem; it is part of combinatorics and applied mathematics.

The value is the weight of the items, and their cost represents how much the item is worth. The knapsack can hold a specified amount of weight, and this limitation cannot be exceeded. In short, you want to maximize the storage capability of the knapsack by packing the most valuable items in it. Sometimes this problem is told in the form of a robbery. Obviously, the thief wants the best bang for his buck (his effort).

Let's say the weight of the items are W1, W2, ... Wk, ... Wn and their cost is C1, C2, ... Ck, ... Cn, respectively; the capacity of the knapsack is specified as K. Now we have the following mathematical formula to calculate the upper bound [UB]. Check it out!

Right after this point we can already present the pseudocode of the algorithm.

Procedure knapsack:

Initialize root;

PQ <- root;

max_cost := root.cost;

while PQ not equal do

current <- PQ;

if (current.bound > max_cost) then

create left_child := next item;

if (left_child.cost > max_cost)

max_cost := left_child.cost;

update best_solution;

end if;

if (left_child.bound > max_cost)

PQ <- left_child;

end if;

create right_child; // it skips packing the next item

if (right_child.bound > max_cost)

PQ <- right_child;

end if;

end if;

end while;

return best_solution and its cost;

end procedure;

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