Add Dart solution for Length of Last Word

dart/length_of_last_word.dart

@@ -0,0 +1,23 @@
+/*
+Given a string s consisting of words and spaces, return the length of the last word in the string.
+
+A word is a maximal substring consisting of non-space characters only.
+*/
+
+class Solution {
+  int lengthOfLastWord(String s) {
+    int index = s.length - 1;
+    int length = 0;
+
+    while (index >= 0 && s[index] == ' ') {
+      index--;
+    }
+
+    while (index >= 0 && s[index] != ' ') {
+      length++;
+      index--;
+    }
+
+    return length;
+  }
+}