1905-count-sub-islands.js

var countSubIslands = function(grid1, grid2) {
    let ROWS = grid1.length, COLS = grid1[0].length;
    let visit = new Set();
    
    const dfs = function(r, c) {
        let flatCoord = r*COLS + c;
        if (
            r < 0
            || c < 0
            || r == ROWS
            || c == COLS
            || grid2[r][c] == 0
            || visit.has(flatCoord)
        )
            return true;
        
        visit.add(flatCoord);
        let res = true;
        if(grid1[r][c] == 0)
            res = false;
        
        res = dfs(r - 1, c) && res;
        res = dfs(r + 1, c) && res;
        res = dfs(r, c - 1) && res;
        res = dfs(r, c + 1) && res;
        return res;
    };
    
    let count = 0;
    for(let r = 0; r < ROWS; r++)
        for(let c = 0; c < COLS; c++)
            if(grid2[r][c] && !visit.has(r*COLS + c) && dfs(r, c))
                count += 1;
    return count;
};