adding string iterator problem

lectures/09_iterators_linked_lists/README.md

@@ -162,4 +162,5 @@ also defined.
 ## 9.9 Leetcode Exercises
 
 - [Leetcode problem 27: Remove Element](https://leetcode.com/problems/remove-element/). Solution: [p27_removeelement.cpp](../../leetcode/p27_removeelement.cpp)
-- [Leetcode problem 283: Remove Zeroes](https://leetcode.com/problems/move-zeroes/). Solution: [p283_movezeroes.cpp](../../leetcode/p283_movezeroes.cpp)
+- [Leetcode problem 58: Length of Last Word](https://leetcode.com/problems/length-of-last-word/). Solution: [p58_lengthoflastword.cpp](../../leetcode/p58_lengthoflastword.cpp)
+- [Leetcode problem 283: Move Zeroes](https://leetcode.com/problems/move-zeroes/). Solution: [p283_movezeroes.cpp](../../leetcode/p283_movezeroes.cpp)

leetcode/p58_lengthoflastword.cpp

@@ -0,0 +1,32 @@
+// demonstration of using an iterator to traverse a string
+
+class Solution {
+public:
+    int lengthOfLastWord(string s) {
+        string::iterator itr = s.begin();
+        vector<string> words;
+        string word = "";
+        while(itr != s.end()){
+            // skip leading spaces
+            while(itr != s.end() && *itr == ' '){
+                itr++;
+            }
+
+            // remember we still need to check whether itr reaches the end or not; if we don't check, we may get a stack buffer overflow issue.
+            while(itr != s.end() && *itr != ' '){
+                // append this letter to the end of the word
+                word = word + *itr;
+                itr++;
+            }
+            // word is now complete, store it in words.
+            // caution: word may be empty because of the spaces at the end of s.
+            if(!word.empty()){
+                words.push_back(word);
+                // reset word
+                word = "";
+            }
+        }
+        word = words.back();
+        return word.length();
+    }
+};