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A map of the 24 permutations and the 23 swaps used in Heap's algorithm permuting the four letters A (amber), B (blue), C (cyan) and D (dark red) Wheel diagram of all permutations of length = generated by Heap's algorithm, where each permutation is color-coded (1=blue, 2=green, 3=yellow, 4=red).
The usual way to prove that there are n! different permutations of n objects is to observe that the first object can be chosen in n different ways, the next object in n − 1 different ways (because choosing the same number as the first is forbidden), the next in n − 2 different ways (because there are now 2 forbidden values), and so forth.
The Steinhaus–Johnson–Trotter algorithm follows this structure: the sequence of permutations it generates consists of ()! blocks of permutations, so that within each block the permutations agree on the ordering of the numbers from 1 to and differ only in the position of . The blocks themselves are ordered recursively, according to the ...
To convert an inversion table d n, d n−1, ..., d 2, d 1 into the corresponding permutation, one can traverse the numbers from d 1 to d n while inserting the elements of S from largest to smallest into an initially empty sequence; at the step using the number d from the inversion table, the element from S inserted into the sequence at the ...
As for the equal probability of the permutations, it suffices to observe that the modified algorithm involves (n−1)! distinct possible sequences of random numbers produced, each of which clearly produces a different permutation, and each of which occurs—assuming the random number source is unbiased—with equal probability.
Another way to see this is to rename h 1 to h i, where the derangement is more explicit: for any j from 2 to n, P j cannot receive h j. P i receives h 1. In this case the problem reduces to n − 2 people and n − 2 hats, because P 1 received h i ' s hat and P i received h 1 's hat, effectively putting both out of further consideration.
In the initial problem, the 100 prisoners are successful if the longest cycle of the permutation has a length of at most 50. Their survival probability is therefore equal to the probability that a random permutation of the numbers 1 to 100 contains no cycle of length greater than 50. This probability is determined in the following.
In computer science, bogosort [1] [2] (also known as permutation sort and stupid sort [3]) is a sorting algorithm based on the generate and test paradigm. The function successively generates permutations of its input until it finds one that is sorted. It is not considered useful for sorting, but may be used for educational purposes, to contrast ...