Update and rename lengthOfLongestSubstring.cpp to longest-substring-without-repeating-characters.cpp

Author: kamyu104

C++/lengthOfLongestSubstring.cpp

@@ -0,0 +1,25 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    int lengthOfLongestSubstring(string s) {
+        // Record the last occurrence of each char.
+        unordered_map<char, size_t> last_occurrence;
+        size_t starting_idx = 0, ans = 0;
+        for (size_t i = 0; i < s.size(); ++i) {
+            auto it(last_occurrence.find(s[i]));
+            if (it == last_occurrence.cend()) {
+                last_occurrence.emplace_hint(it, s[i], i);
+            } else {  // s[i] appeared before. Check its validity.
+                if (it->second >= starting_idx) {
+                    ans = max(ans, i - starting_idx);
+                    starting_idx = it->second + 1;
+                }
+                it->second = i;
+            }
+        }
+        ans = max(ans, s.size() - starting_idx);
+        return ans;
+    }
+};