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export default function islandPerimeter(grid: number[][]): number {    const m = grid.length;    if (m === 0) return 0;    const n = grid[0].length;    if (n === 0) return 0;    let perimeter = 0;    for (let i = 0; i < grid.length; i++) {        for (let j = 0; j < grid[0].length; j++) {            if (grid[i][j] == 1) {                perimeter += 4;
                if (i - 1 >= 0 && grid[i - 1][j] === 1) perimeter--;                if (j - 1 >= 0 && grid[i][j - 1] === 1) perimeter--;                if (i + 1 <= m - 1 && grid[i + 1][j] === 1) perimeter--;                if (j + 1 <= n - 1 && grid[i][j + 1] === 1) perimeter--;            }        }    }
    return perimeter;}