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September 21, 2018 15:55
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Array combinations, permutations and arrangements
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// permutation: Permutação | |
// P(n) = n! | |
// Exemplo: número de anagramas da palavra LIVRO = P(5) = n! | |
// Possibilidades de uma fila de 25 pessoas = P(25) = 25! | |
// combination: Combinação | |
// C(p,n) = = n! / p!(n - p)! | |
// Exemplo: formar comissão de 3 pessoas escolhidas entre 10 pessoas. C(3,10) = 10! / 3!(10 - 3)! | |
// arrangement: Arranjo | |
// Note que permutação é um caso particular de arranjo onde p = n | |
// A(p,n) = n! / (n - p)! | |
// Exemplo: pódio 20 competidores devem ser organizados em 3 lugares e a ordem importa. A(3,20) = 20! / (20 - 3)! | |
// Note também que o arranjo nada mais é do que uma combinação seguida da permutação do resultado da combinação. | |
// Usage: | |
// console.log([1,2,3,4].combinations(2)); | |
// >> [ [ 1, 2 ], [ 1, 3 ], [ 1, 4 ], [ 2, 3 ], [ 2, 4 ], [ 3, 4 ] ] | |
// console.log([1,2,3,4].permutations()); | |
// >> [ [ 1, 2, 3, 4 ], | |
// >> [ 1, 2, 4, 3 ], | |
// >> [ 1, 3, 2, 4 ], | |
// >> [ 1, 3, 4, 2 ], | |
// >> [ 1, 4, 2, 3 ], | |
// >> [ 1, 4, 3, 2 ], | |
// >> [ 2, 1, 3, 4 ], | |
// >> [ 2, 1, 4, 3 ], | |
// >> [ 2, 3, 1, 4 ], | |
// >> [ 2, 3, 4, 1 ], | |
// >> [ 2, 4, 1, 3 ], | |
// >> [ 2, 4, 3, 1 ], | |
// >> [ 3, 1, 2, 4 ], | |
// >> [ 3, 1, 4, 2 ], | |
// >> [ 3, 2, 1, 4 ], | |
// >> [ 3, 2, 4, 1 ], | |
// >> [ 3, 4, 1, 2 ], | |
// >> [ 3, 4, 2, 1 ], | |
// >> [ 4, 1, 2, 3 ], | |
// >> [ 4, 1, 3, 2 ], | |
// >> [ 4, 2, 1, 3 ], | |
// >> [ 4, 2, 3, 1 ], | |
// >> [ 4, 3, 1, 2 ], | |
// >> [ 4, 3, 2, 1 ] ] | |
// console.log([1,2,3,4].arrangements(2)); | |
// >> [ [ 1, 2 ], | |
// >> [ 2, 1 ], | |
// >> [ 1, 3 ], | |
// >> [ 3, 1 ], | |
// >> [ 1, 4 ], | |
// >> [ 4, 1 ], | |
// >> [ 2, 3 ], | |
// >> [ 3, 2 ], | |
// >> [ 2, 4 ], | |
// >> [ 4, 2 ], | |
// >> [ 3, 4 ], | |
// >> [ 4, 3 ] ] | |
Array.prototype.combinations = function(p) { | |
var combs, head, tailcombs; | |
if (p > this.length || p <= 0) { | |
return []; | |
} | |
if (p == this.length) { | |
return [this]; | |
} | |
if (p == 1) { | |
combs = []; | |
for (i = 0; i < this.length; i++) { | |
combs.push([this[i]]); | |
} | |
return combs; | |
} | |
combs = []; | |
for (var i = 0; i < this.length - p + 1; i++) { | |
head = this.slice(i, i+1); | |
tailcombs = this.slice(i + 1).combinations(p - 1); | |
for (var j = 0; j < tailcombs.length; j++) { | |
combs.push(head.concat(tailcombs[j])); | |
} | |
} | |
return combs; | |
}; | |
Array.prototype.permutations = function() { | |
if (this.length === 0) { | |
return [[]]; | |
} | |
var result = []; | |
for (var i = 0; i < this.length; i++) { | |
var copy = Object.create(this); | |
var head = copy.splice(i, 1); | |
var rest = copy.permutations(); | |
for (var j = 0; j < rest.length; j++) { | |
var next = head.concat(rest[j]); | |
result.push(next); | |
} | |
} | |
return result; | |
}; | |
Array.prototype.arrangements = function(p) { | |
var combinations = this.combinations(p); | |
var arrangements = []; | |
combinations.forEach(function(combination) { | |
var ps = combination.permutations(); | |
ps.forEach(function(p) { | |
arrangements.push(p); | |
}); | |
}); | |
return arrangements; | |
}; | |
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