Number Of Distinct Islands

if (!grid || !grid.length) return 0;

let numRows = grid.length,
    numCols = grid[0].length,
    LAND = 1, VISITED = 2;

function markAndVisit(row, col, island = [], level = 0) {
    if (grid[row][col] === LAND) {
        grid[row][col] = VISITED;
        island.push('X' + level);

        // up
        if (row > 0 && grid[row - 1][col] === LAND) {
            island.push('U' + level);
            markAndVisit(row - 1, col, island, level + 1);
        }

        // down
        if (row < numRows - 1 && grid[row + 1][col] === LAND) {
            island.push('D' + level);
            markAndVisit(row + 1, col, island, level + 1);
        }

        // left
        if (col > 0 && grid[row][col - 1] === LAND) {
            island.push('L' + level);
            markAndVisit(row, col - 1, island, level + 1);
        }

        // right
        if (col < numCols - 1 && grid && grid[row][col + 1] === LAND) {
            island.push('R' + level);
            markAndVisit(row, col + 1, island, level + 1);
        }
    }

    return island;
}

let islands = new Set();
for (let row = 0; row < numRows;row++) {
    for (let col = 0; col < numCols;col++) {
        if (grid[row][col] === LAND) {
            let island = markAndVisit(row, col);
            // console.log(island);
            if (island.length) islands.add(island.join(''));
        }
    }
}

// console.table(grid);
return islands.size;