Grid BFS/DFS Patterns

const dirs = [[0,1],[0,-1],[1,0],[-1,0]]; // 4-directional
// const dirs = [[0,1],[0,-1],[1,0],[-1,0],[1,1],[1,-1],[-1,1],[-1,-1]]; // 8-directional

const inBounds = (r, c, m, n) => r >= 0 && r < m && c >= 0 && c < n;

// DFS flood fill — mark connected region
function dfs(grid, r, c, visited) {
    if (!inBounds(r,c,grid.length,grid[0].length)) return;
    if (visited[r][c] || grid[r][c] === 0) return;
    visited[r][c] = true;
    for (const [dr,dc] of dirs) dfs(grid, r+dr, c+dc, visited);
}

// BFS shortest path to any target
function bfs(grid, startR, startC) {
    const m=grid.length, n=grid[0].length;
    const dist = Array.from({length:m},()=>new Array(n).fill(-1));
    dist[startR][startC] = 0;
    let queue = [[startR, startC]];
    while (queue.length) {
        const next = [];
        for (const [r,c] of queue) {
            for (const [dr,dc] of dirs) {
                const nr=r+dr, nc=c+dc;
                if (!inBounds(nr,nc,m,n) || dist[nr][nc] !== -1 || grid[nr][nc] === 0) continue;
                dist[nr][nc] = dist[r][c] + 1;
                next.push([nr,nc]);
            }
        }
        queue = next;
    }
    return dist;
}

// Multi-source BFS — distance from nearest source
function multiSourceBFS(grid, sources) {
    const m=grid.length, n=grid[0].length;
    const dist = Array.from({length:m},()=>new Array(n).fill(Infinity));
    const queue = [];
    for (const [r,c] of sources) { dist[r][c] = 0; queue.push([r,c]); }
    let i = 0;
    while (i < queue.length) {
        const [r,c] = queue[i++];
        for (const [dr,dc] of dirs) {
            const nr=r+dr, nc=c+dc;
            if (!inBounds(nr,nc,m,n)||dist[nr][nc]!==Infinity) continue;
            dist[nr][nc] = dist[r][c] + 1;
            queue.push([nr,nc]);
        }
    }
    return dist;
}