1+ /**
2+ * @param {string[] } deadends
3+ * @param {string } target
4+ * @return {number }
5+ */
6+ var openLock = function ( deadends , target ) {
7+
8+ // General approach:
9+ // Start at the end, mark that spot to be 0 away from target
10+ // Find all the valid neighbors through bfs, mark those as 1
11+ // Find all _their_ valid neighbors, mark those as ++ etc
12+ // Until we find 0000. Whatever we mark that as is the number. BFS will guarantee it's the shortest path
13+
14+ let q = [ target ] ; // our BFS Queue
15+ let mem = { } ; // to keep track what we already have visited
16+ mem [ target ] = 0 ; // starting distance of the end
17+
18+ // Helper function that given a position, will generate all the numbers we
19+ // can create in 1 move;
20+ let getNextPositions = function ( pos ) {
21+ // one above, one below
22+ let dir = [ - 1 , 1 ] ;
23+ let arr = pos . split ( '' ) ;
24+ let positions = [ ] ;
25+ let i , j ;
26+
27+ for ( j = 0 ; j < 2 ; j ++ ) {
28+ let next = '' ;
29+ // for each number in the position
30+ for ( i = 0 ; i < 4 ; i ++ ) {
31+ // logic is not just +1 -1, have to deal with wrapping around
32+ let n = ( 10 + parseInt ( arr [ i ] , 10 ) + dir [ j ] ) % 10 ;
33+ // clone to not ruin our array for the next number
34+ let next = [ ...arr ] ;
35+ // set our 1 change
36+ next [ i ] = n ;
37+ positions . push ( next . join ( '' ) ) ;
38+ }
39+ }
40+ return positions ;
41+ }
42+
43+ while ( q . length ) {
44+ // dequeue a position to check out
45+ let pos = q . shift ( ) ;
46+
47+ // if it's 0000 we're done. BFS guarantees it's the shortest possible
48+ if ( pos === '0000' ) {
49+ return mem [ pos ] ;
50+ } else {
51+ let next = getNextPositions ( pos ) ;
52+ next . forEach ( function ( n ) {
53+ // if we haven't seen n before, and it's not a dead end,
54+ if ( mem [ n ] === undefined && ! deadends . includes ( n ) ) {
55+ // mark the distance and enqueue to check out next
56+ mem [ n ] = mem [ pos ] + 1 ;
57+ q . push ( n ) ;
58+ }
59+ } )
60+ }
61+ }
62+ // if we end up here, we couldn't find it
63+ return - 1 ;
64+ } ;
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