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Frobenius coin problem with 2-pence and 5-pence coins visualised as graphs: Sloping lines denote graphs of 2x+5y=n where n is the total in pence, and x and y are the non-negative number of 2p and 5p coins, respectively.
In computational complexity theory, the 3SUM problem asks if a given set of real numbers contains three elements that sum to zero. A generalized version, k-SUM, asks the same question on k elements, rather than simply 3. 3SUM can be easily solved in () time, and matching (⌈ / ⌉) lower bounds are known in some specialized models of computation (Erickson 1999).
In the th step, it computes the subarray with the largest sum ending at ; this sum is maintained in variable current_sum. [note 3] Moreover, it computes the subarray with the largest sum anywhere in […], maintained in variable best_sum, [note 4] and easily obtained as the maximum of all values of current_sum seen so far, cf. line 7 of the ...
The sum is a sum over all partitions of p. Another exact nested sum expansion for these Stirling numbers is computed by elementary symmetric polynomials corresponding to the coefficients in x {\displaystyle x} of a product of the form ( 1 + c 1 x ) ⋯ ( 1 + c n − 1 x ) {\displaystyle (1+c_{1}x)\cdots (1+c_{n-1}x)} .
The rule of sum is an intuitive principle stating that if there are a possible outcomes for an event (or ways to do something) and b possible outcomes for another event (or ways to do another thing), and the two events cannot both occur (or the two things can't both be done), then there are a + b total possible outcomes for the events (or total possible ways to do one of the things).
Another way to combine two (disjoint) posets is the ordinal sum [12] (or linear sum), [13] Z = X ⊕ Y, defined on the union of the underlying sets X and Y by the order a ≤ Z b if and only if: a, b ∈ X with a ≤ X b, or; a, b ∈ Y with a ≤ Y b, or; a ∈ X and b ∈ Y. If two posets are well-ordered, then so is their ordinal sum. [14]
For any pair of positive integers n and k, the number of k-tuples of positive integers whose sum is n is equal to the number of (k − 1)-element subsets of a set with n − 1 elements. For example, if n = 10 and k = 4, the theorem gives the number of solutions to x 1 + x 2 + x 3 + x 4 = 10 (with x 1, x 2, x 3, x 4 > 0) as the binomial coefficient
The subset sum problem is a special case of the decision and 0-1 problems where each kind of item, the weight equals the value: =. In the field of cryptography, the term knapsack problem is often used to refer specifically to the subset sum problem. The subset sum problem is one of Karp's 21 NP-complete problems. [2]