Count number of islands

countNumberOfIslands.kt

numIslands(
    grid = arrayOf(
        charArrayOf('1', '1', '1', '1', '0'),
        charArrayOf('1', '1', '0', '1', '0'),
        charArrayOf('1', '1', '0', '0', '0'),
        charArrayOf('0', '0', '0', '0', '0')
    )
)

numIslands(
    grid = arrayOf(
        charArrayOf('1', '1', '0', '0', '0'),
        charArrayOf('1', '1', '0', '0', '0'),
        charArrayOf('0', '0', '1', '0', '0'),
        charArrayOf('0', '0', '0', '1', '1')
    )
)

fun numIslands(grid: Array<CharArray>): Int {
    var islandCount = 0
    grid.forEachIndexed { rowIndex, chars ->
        chars.forEachIndexed { colIndex, c ->
            // If we found a land, we all adjacent to zero (water) and increase island count by 1
            if (c == '1') {
                islandCount += setAdjacentToZero(rowIndex, colIndex, grid)
            }
        }
    }

    return islandCount
}

fun setAdjacentToZero(rowIndex: Int, colIndex: Int, grid: Array<CharArray>): Int {
    if (rowIndex < 0 || colIndex < 0 || rowIndex >= grid.size || colIndex >= grid[rowIndex].size || grid[rowIndex][colIndex] == '0')
        return 0
        
    grid[rowIndex][colIndex] = '0'
    setAdjacentToZero(rowIndex + 1, colIndex, grid)
    setAdjacentToZero(rowIndex - 1, colIndex, grid)
    setAdjacentToZero(rowIndex, colIndex + 1, grid)
    setAdjacentToZero(rowIndex, colIndex - 1, grid)

    return 1
}