Longest Substring Without Repeating Characters

src/s0003_longest_substring_without_repeating_characters.cpp

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+#include "s0003_longest_substring_without_repeating_characters.hpp"
+
+int Solution::lengthOfLongestSubstring(std::string s) {
+  // index_forward points to the frontmost element
+  // index_backward points to the last repeated element
+  //
+  // for
+  //    check if index_forward pointed element exists in hash map
+  //            if exists, index_backward = max(index_backward, the index of
+  //            this element)
+  //    push
+  //    index_forward += 1
+  //    len = max(index_forward, index_backward)
+  std::map<char, int> map;
+  int index_backward{-1};
+  int index_forward{0};
+  int len{0};
+  for (; index_forward < s.length(); index_forward++) {
+    if (map.count(s[index_forward]) == 1) {
+      index_backward = std::max(index_backward, map.at(s[index_forward]));
+    }
+    map[s[index_forward]] = index_forward;
+    len = std::max(len, index_forward - index_backward);
+  }
+  return len;
+}