Add solution to 374.

Author: ovidiubute

.prettierrc.json

@@ -0,0 +1,6 @@
+{
+  "trailingComma": "es5",
+  "tabWidth": 2,
+  "semi": true,
+  "singleQuote": false
+}

solutions/0374.guess-number-higher-or-lower.js

@@ -0,0 +1,31 @@
+/**
+ * Forward declaration of guess API.
+ * @param {number} num   your guess
+ * @return 	            -1 if num is lower than the guess number
+ *			             1 if num is higher than the guess number
+ *                       otherwise return 0
+ * var guess = function(num) {}
+ */
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var guessNumber = function (n) {
+  let lo = 1,
+    hi = n;
+
+  while (lo <= hi) {
+    let mid = Math.floor((lo + hi) / 2);
+    const g = guess(mid);
+    if (g === 0) {
+      return mid;
+    } else if (g === -1) {
+      hi = mid - 1;
+    } else {
+      lo = mid + 1;
+    }
+  }
+
+  return -1;
+};