1+ const DIRECTIONS = [ [ - 1 , 0 ] , [ 1 , 0 ] , [ 0 , - 1 ] , [ 0 , 1 ] ] ;
2+
3+ const shortestBridge = ( grid ) => {
4+ const rows = grid . length ;
5+ const cols = grid [ 0 ] . length ;
6+
7+ let queue = [ ] ;
8+
9+ const exploreIslandDFS = ( row , col ) => {
10+ if ( row < 0 || row >= rows || col < 0 || col >= cols || grid [ row ] [ col ] !== 1 ) {
11+ return false ;
12+ }
13+
14+ queue . push ( [ row , col ] ) ;
15+ grid [ row ] [ col ] = 2 ;
16+
17+ exploreIslandDFS ( row - 1 , col ) ;
18+ exploreIslandDFS ( row + 1 , col ) ;
19+ exploreIslandDFS ( row , col - 1 ) ;
20+ exploreIslandDFS ( row , col + 1 ) ;
21+
22+ return true ;
23+ } ;
24+
25+ const buildBridgeBFS = ( ) => {
26+ let distance = - 1 ;
27+ let currentQueue = [ ] ;
28+
29+ while ( queue . length ) {
30+ currentQueue = queue ;
31+ queue = [ ] ;
32+
33+ for ( let [ row , col ] of currentQueue ) {
34+ for ( let [ dx , dy ] of DIRECTIONS ) {
35+ const nextRow = row + dx ;
36+ const nextCol = col + dy ;
37+
38+ if (
39+ nextRow >= 0 &&
40+ nextRow < rows &&
41+ nextCol >= 0 &&
42+ nextCol < cols &&
43+ grid [ nextRow ] [ nextCol ] !== 2
44+ ) {
45+ if ( grid [ nextRow ] [ nextCol ] === 1 ) {
46+ return distance + 1 ;
47+ }
48+
49+ queue . push ( [ nextRow , nextCol ] ) ;
50+ grid [ nextRow ] [ nextCol ] = 2 ;
51+ }
52+ }
53+ }
54+
55+ distance ++ ;
56+ }
57+
58+ return - 1 ;
59+ } ;
60+
61+ for ( let i = 0 ; i < rows ; i ++ ) {
62+ for ( let j = 0 ; j < cols ; j ++ ) {
63+ if ( exploreIslandDFS ( i , j ) ) {
64+ return buildBridgeBFS ( ) ;
65+ }
66+ }
67+ }
68+
69+ return - 1 ;
70+ } ;
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