Secret santa permutor

example_output.txt

EAS=>PRB, MP=>AS, R=>E, B=>M
EAS=>PRB, MP=>ES, R=>A, B=>M
EAS=>PRB, MP=>EA, R=>S, B=>M
EAS=>MPR, MP=>EA, R=>B, B=>S
EAS=>MPB, MP=>AR, R=>E, B=>S
EAS=>MPR, MP=>AB, R=>E, B=>S
EAS=>MRB, MP=>EA, R=>P, B=>S
EAS=>MPR, MP=>EB, R=>A, B=>S
EAS=>MPB, MP=>ER, R=>A, B=>S
EAS=>PRB, MP=>EA, R=>M, B=>S
EAS=>PRB, MP=>ES, R=>M, B=>A
EAS=>MPR, MP=>ES, R=>B, B=>A
EAS=>MPR, MP=>SB, R=>E, B=>A
EAS=>MPB, MP=>SR, R=>E, B=>A
EAS=>MRB, MP=>ES, R=>P, B=>A
EAS=>MPR, MP=>EB, R=>S, B=>A
EAS=>MPB, MP=>ER, R=>S, B=>A
EAS=>MRB, MP=>EA, R=>S, B=>P
EAS=>MRB, MP=>AS, R=>E, B=>P
EAS=>MRB, MP=>ES, R=>A, B=>P
EAS=>MPB, MP=>ES, R=>A, B=>R
EAS=>MPB, MP=>EA, R=>S, B=>R
EAS=>MPB, MP=>AS, R=>E, B=>R
EAS=>MRB, MP=>AS, R=>P, B=>E
EAS=>MPB, MP=>SR, R=>A, B=>E
EAS=>MPR, MP=>SB, R=>A, B=>E
EAS=>MPR, MP=>AB, R=>S, B=>E
EAS=>MPB, MP=>AR, R=>S, B=>E
EAS=>PRB, MP=>AS, R=>M, B=>E
EAS=>MPR, MP=>AS, R=>B, B=>E

xmas_permutor.js

function* permutations(N) {
	var arr=Array(N).fill(0).map((x,y)=>y); //Fill with 0,1,2,3,4....N-1
	function swap(i,j) { var tmp=arr[i]; arr[i]=arr[j]; arr[j]=tmp; }
	var c=Array(N).fill(0);
	yield arr.slice();  //start with first permutation

	for(var i=0;i<N;) { //Heap's algorithm
		if (c[i]<i) {
			swap(i%2?c[i]:0,i);
			yield arr.slice();
			c[i]++; i=0;
		} else { 
			c[i]=0; i++;
		}
	}	
}

var people = ['E','A','S','M','P','R','B'];
var fam = [0,0,0,1,1,2,3];
var N = 7;

for (var P of permutations(N)) {
	if (P.some((t,f)=>(f==t))) continue; //Can't give to self
	if (P.some((t,f)=>(fam[f]==fam[t]))) continue; //Can't give to same family.
	if (P.some((t,f)=>{
		//console.log("From: "+f+" To: "+t+" To-: "+P[f-1]+" Fam:"+fam[f]+"-"+fam[f-1]);
		return f>0 && fam[f-1]==fam[f] && P[f-1]>t;
	})) continue; //Take only first permutation of recipients from a given family

	//Format nicely
	var byfam=[];
	for(var i=0;i<N;i++) {
		var g = fam[i];
		byfam[g]||(byfam[g]={f:[],t:[]});
		byfam[g].f.push(people[i]);
		byfam[g].t.push(people[P[i]]);
	}
	console.log( byfam.map(g=>g.f.join('')+'=>'+g.t.join('')).join(', '));		
	//console.log(P);
}