[프로그래머스 Level 2] 미로 탈출

function solution(maps) {
    const m = maps.length;
    const n = maps[0].length;
    const dx = [0, 0, -1, 1];
    const dy = [1, -1, 0, 0];
 
    let start, exit, lever;
 
    maps = maps.map((row, i) =>
        row.split('').map((node, j) => {
            if(node === 'S') start = [i, j];
            if(node === 'L') lever = [i, j];
            if(node === 'E') exit = [i, j];
            if(node === 'X') return 0;
            return 1;
        })
    );
 
    function bfs(matrix, start, end){
        const q = [ start ];
        const visited = Array.from({ length: m }, () => new Array(n).fill(0));
        const distance = Array.from({ length: m }, () => Array(n).fill(Infinity));
 
        distance[start[0]][start[1]] = 0;
 
        while(q.length){
            const [y, x] = q.shift();
 
            if(visited[y][x] === 0){
                visited[y][x] = 1;
 
                if(y === end[0] && x === end[1]){
                    return distance[y][x];
                }
 
                dx.forEach((_, i) => {
                    const nx = Math.min(Math.max(x + dx[i], 0), n - 1);
                    const ny = Math.min(Math.max(y + dy[i], 0), m - 1);
 
                    if(matrix[ny][nx] && !visited[ny][nx]){
                        distance[ny][nx] = distance[y][x] + 1;
                        q.push([ny, nx]);
                    }
                });
            }
        }
 
        return -1;
    }
 
    // 시작 지점에서 레버까지 최단거리
    const toLever = bfs(maps, start, lever);
    // 레버에서 출구까지 최단거리
    const fromLever = bfs(maps, lever, exit);
 
    if(toLever === -1 || fromLever === -1){
        return -1;
    }
 
    return toLever + fromLever;
}