added description

Author: mauricechouam

Find Smallest Letter Greater Than Target/code.js

@@ -0,0 +1,21 @@
+/*
+ * @param {character[]} letters
+ * @param {character} target
+ * @return {character}
+ */
+var nextGreatestLetter = function(letters, target) {
+    
+    if (letters[0] > target || target >= letters[letters.length - 1]) return letters[0]
+    let s = 0
+    let e = letters.length - 1
+    while (s < e) {
+        let mid = Math.trunc((e + s) / 2)
+        if (target < letters[mid]) {
+            e = mid
+        } else {
+            s = mid + 1
+        }
+    }
+    return letters[s]
+};
+