number of islands solution

Author: yhkee0404

number-of-islands/yhkee0404.go

@@ -0,0 +1,40 @@
+var DRCS = [][]int{
+    {0, -1,},
+    {0, 1,},
+    {-1, 0,},
+    {1, 0,},
+}
+
+func numIslands(grid [][]byte) int {
+    visited := make([][]bool, len(grid)) // S(n) = O(n)
+    for i, row := range grid {
+        visited[i] = make([]bool, len(row))
+    }
+    ans := 0
+    stack := [][]int{}
+    for i, row := range grid {
+        for j, c := range row {
+            if visited[i][j] || c == '0' {
+                continue
+            }
+            ans++
+            visited[i][j] = true
+            stack = append(stack, []int{i, j})
+            for len(stack) != 0 { // T(n) = O(n)
+                u := stack[len(stack) - 1]
+                stack = stack[: len(stack) - 1]
+                for _, drc := range DRCS {
+                    x := u[0] + drc[0]
+                    y := u[1] + drc[1]
+                    if x == -1 || x == len(grid) || y == -1 || y == len(row) ||
+                            grid[x][y] == '0' || visited[x][y] {
+                        continue
+                    }
+                    visited[x][y] = true
+                    stack = append(stack, []int{x, y})
+                }
+            }
+        }
+    }
+    return ans
+}