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An issue tree, also called logic tree, is a graphical breakdown of a question that dissects it into its different components vertically and that progresses into details as it reads to the right. [1]: 47 Issue trees are useful in problem solving to identify the root causes of a problem as well as to identify its potential solutions. They also ...
the associated and–or tree is a set of labelled nodes such that: The root of the tree is a node labelled by P 0. For every node N labelled by a problem or sub-problem P and for every method of the form P if P 1 and ... and P n, there exists a set of children nodes N 1, ..., N n of the node N, such that each node N i is labelled by P i. The ...
Clearly, a #P problem must be at least as hard as the corresponding NP problem, since a count of solutions immediately tells if at least one solution exists, if the count is greater than zero. Surprisingly, some #P problems that are believed to be difficult correspond to easy (for example linear-time) P problems. [18]
On the one hand, there are many problems that have a solution space just as large, but can be solved in polynomial time (for example minimum spanning tree). On the other hand, there are NP-problems with at most one solution that are NP-hard under randomized polynomial-time reduction (see Valiant–Vazirani theorem).
In the modern era, it is often used as an example problem for various computer programming techniques. The eight queens puzzle is a special case of the more general n queens problem of placing n non-attacking queens on an n×n chessboard. Solutions exist for all natural numbers n with the exception of n = 2 and n = 3.
Solution of a travelling salesman problem: the black line shows the shortest possible loop that connects every red dot. In the theory of computational complexity, the travelling salesman problem (TSP) asks the following question: "Given a list of cities and the distances between each pair of cities, what is the shortest possible route that visits each city exactly once and returns to the ...
Equivalently, what is the decision tree complexity of the MST problem? The optimal algorithm to compute MSTs is known , but it relies on decision trees, so its complexity is unknown. Gilbert–Pollak conjecture : Is the Steiner ratio of the Euclidean plane equal to 2 / 3 {\displaystyle 2/{\sqrt {3}}} ?
For example, the problem of factoring "Given a positive integer n, find a nontrivial prime factor of n." is a computational problem that has a solution, as there are many known integer factorization algorithms. A computational problem can be viewed as a set of instances or cases together with a, possibly empty, set of solutions for every ...