go: add «2017. Grid Game»

URL:	https://leetcode.com/problems/grid-game/
Signed-off-by: Matej Focko <me@mfocko.xyz>

go/grid-game.go

@@ -0,0 +1,20 @@
+package main
+
+func gridGame(grid [][]int) int64 {
+	prefix, suffix := int64(0), int64(0)
+
+	// first row gets precomputed separately
+	for _, points := range grid[0] {
+		prefix += int64(points)
+	}
+
+	minSum := int64(10000000001)
+	for turn, first := range grid[0] {
+		prefix -= int64(first)
+
+		minSum = min(minSum, max(prefix, suffix))
+		suffix += int64(grid[1][turn])
+	}
+
+	return minSum
+}