add new solutions

solutions/3/q374/solution.go

@@ -0,0 +1,22 @@
+package q374
+
+func guess(num int) int { panic("stub") }
+
+func guessNumber(n int) int {
+	l, r := 1, n+1
+
+	for l < r {
+		m := (l + r) / 2
+		switch guess(m) {
+		case -1: // too high
+			r = m
+		case 1: // too low
+			l = m + 1
+		case 0:
+			return m
+		}
+	}
+	return -1
+}
+
+var _ = guessNumber