1+ 2+ // let permutation = [];
3+ // const permutate = (arr) => {
4+ // for (let i = 0; i < arr.length - 1; i++) {
5+ // let current = arr[i];
6+ 7+ // let next = arr[i + 1]
8+ // arr[i] = next;
9+ // arr[i + 1] = current;
10+ // permutation.push(arr.map(x=>x));
11+ // arr[i + 1] = next;
12+ // arr[i] = current;
13+ 14+ // }
15+ // }
16+ 17+ // let arr = [1, 2, 3]
18+ // permutate(arr)
19+ // console.log(permutation);
20+ 21+ 22+ let permArr = [ ] ,
23+ usedChars = [ ] ;
24+ function permute ( input , diff ) {
25+ var i , ch ;
26+ for ( i = 0 ; i < input . length ; i ++ ) {
27+ // fixed 1, then process [2,3]
28+ ch = input . splice ( i , 1 ) [ 0 ] ;
29+ // usedchars [1]
30+ usedChars . push ( ch ) ;
31+ if ( input . length == 0 ) {
32+ let bool = true ;
33+ for ( let k = 0 ; k < usedChars . length ; k ++ ) {
34+ if ( Math . abs ( ( usedChars [ k ] - ( k + 1 ) ) ) !== diff ) {
35+ bool = false ;
36+ break ;
37+ }
38+ }
39+ // console.log(usedChars);
40+ if ( bool ) {
41+ return usedChars ;
42+ }
43+ }
44+ // processing [2,3]
45+ let res = permute ( input , diff )
46+ if ( res . length > 0 ) {
47+ return res ;
48+ }
49+ 50+ input . splice ( i , 0 , ch ) ;
51+ usedChars . pop ( ) ;
52+ }
53+ return [ ] ;
54+ } ;
55+ 56+ function validate ( arr , diff ) {
57+ for ( let k = 0 ; k < arr . length ; k ++ ) {
58+ let index = k + 1 ;
59+ let ithElement = arr [ k ] ;
60+ if ( Math . abs ( index - ithElement ) !== diff ) {
61+ return [ ] ;
62+ }
63+ }
64+ return arr ;
65+ }
66+ 67+ function permute2 ( permutation , diff ) {
68+ let length = permutation . length ,
69+ c = new Array ( length ) . fill ( 0 ) ,
70+ i = 1 , k , p ;
71+ let arr = permutation . slice ( ) ;
72+ if ( validate ( arr , diff ) . length > 0 )
73+ return arr ;
74+ 75+ while ( i < length ) {
76+ if ( c [ i ] < i ) {
77+ k = i % 2 && c [ i ] ;
78+ p = permutation [ i ] ;
79+ permutation [ i ] = permutation [ k ] ;
80+ permutation [ k ] = p ;
81+ ++ c [ i ] ;
82+ i = 1 ;
83+ arr = permutation . slice ( ) ;
84+ if ( validate ( arr , diff ) . length > 0 )
85+ return arr ;
86+ 87+ } else {
88+ c [ i ] = 0 ;
89+ ++ i ;
90+ }
91+ }
92+ return [ ] ;
93+ }
94+ n = 10 ;
95+ k = 5 ;
96+ 97+ let numbers = Array . from ( Array ( n ) , ( _ , i ) => i + 1 ) ;
98+ 99+ console . log ( ( permute2 ( numbers , k ) ) ) ;
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