go: add «2658. Maximum Number of Fish in a Grid»

URL:	https://leetcode.com/problems/maximum-number-of-fish-in-a-grid/
Signed-off-by: Matej Focko <me@mfocko.xyz>

go/maximum-number-of-fish-in-a-grid.go

@@ -0,0 +1,42 @@
+package main
+
+func findMaxFish(grid [][]int) int {
+	DIRECTIONS := [][]int{
+		{0, 1},
+		{0, -1},
+		{1, 0},
+		{-1, 0},
+	}
+
+	width, height := len(grid[0]), len(grid)
+	inRange := func(y, x int) bool {
+		return y >= 0 && y < height && x >= 0 && x < width
+	}
+
+	var dfs func(int, int) int
+	dfs = func(y, x int) int {
+		if !inRange(y, x) || grid[y][x] == 0 {
+			return 0
+		}
+
+		// record found fish and reset to zero to mark as irrelevant
+		found := grid[y][x]
+		grid[y][x] = 0
+
+		for _, dir := range DIRECTIONS {
+			dy, dx := dir[0], dir[1]
+			found += dfs(y+dy, x+dx)
+		}
+
+		return found
+	}
+
+	foundMax := 0
+	for y, row := range grid {
+		for x, _ := range row {
+			foundMax = max(foundMax, dfs(y, x))
+		}
+	}
+
+	return foundMax
+}