go: add «399. Evaluate Division»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/evaluate-division.go

@@ -0,0 +1,75 @@
+package main
+
+type Expression struct {
+	variable string
+	constant float64
+}
+
+func calcEquation(equations [][]string, values []float64, queries [][]string) []float64 {
+	process := func() map[string]([]Expression) {
+		g := make(map[string]([]Expression), 0)
+
+		for i, eq := range equations {
+			x, y := eq[0], eq[1]
+
+			if g[x] == nil {
+				g[x] = make([]Expression, 0)
+			}
+			g[x] = append(g[x], Expression{
+				variable: y,
+				constant: values[i],
+			})
+
+			if g[y] == nil {
+				g[y] = make([]Expression, 0)
+			}
+			g[y] = append(g[y], Expression{
+				variable: x,
+				constant: 1 / values[i],
+			})
+		}
+
+		return g
+	}
+	graph := process()
+
+	var dfs func(map[string]bool, string, string, float64, *float64)
+	dfs = func(visited map[string]bool, src, dest string, product float64, result *float64) {
+		if visited[src] {
+			return
+		}
+		visited[src] = true
+
+		if src == dest {
+			*result = product
+			return
+		}
+
+		neighbors, hasNeighbors := graph[src]
+		if !hasNeighbors {
+			return
+		}
+
+		for _, nextSrc := range neighbors {
+			dfs(visited, nextSrc.variable, dest, product*nextSrc.constant, result)
+		}
+	}
+
+	getResult := func(src, dst string) float64 {
+		result := -1.0
+
+		visited := make(map[string]bool, 0)
+		if graph[src] != nil {
+			dfs(visited, src, dst, 1.0, &result)
+		}
+
+		return result
+	}
+
+	results := make([]float64, len(queries))
+	for i, query := range queries {
+		results[i] = getResult(query[0], query[1])
+	}
+
+	return results
+}