g0101_0200.s0200_number_of_islands.solution.go Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

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package s0200_number_of_islands

// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Depth_First_Search
// #Breadth_First_Search #Matrix #Union_Find
// #Algorithm_II_Day_6_Breadth_First_Search_Depth_First_Search
// #Graph_Theory_I_Day_1_Matrix_Related_Problems #Level_1_Day_9_Graph/BFS/DFS #Udemy_Graph
// #Big_O_Time_O(M*N)_Space_O(M*N) #2024_03_22_Time_4_ms_(76.94%)_Space_4_MB_(44.10%)

func numIslands(grid [][]byte) int {
	islands := 0
	if grid != nil && len(grid) != 0 && len(grid[0]) != 0 {
		for i := range grid {
			for j := range grid[i] {
				if grid[i][j] == '1' {
					dfs(grid, i, j)
					islands++
				}
			}
		}
	}
	return islands
}

func dfs(grid [][]byte, x, y int) {
	if x < 0 || len(grid) <= x || y < 0 || len(grid[0]) <= y || grid[x][y] != '1' {
		return
	}
	grid[x][y] = 'x'
	dfs(grid, x+1, y)
	dfs(grid, x-1, y)
	dfs(grid, x, y+1)
	dfs(grid, x, y-1)
}