Create Longest_Substring_Without_Repeating_Characters.cpp

others/longest_substring_without_repeating_characters.cpp

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+/**
+ * @file
+ * @brief Solution for Longest Substring Without Repeating Characters problem.
+ * @details
+ * Problem link: https://leetcode.com/problems/longest-substring-without-repeating-characters/description/
+ * 
+ * Intuition:
+ * 1) The intuition is straightforward and simple. We track the frequency of characters.
+ * 2) Since we can't use a string to track the longest substring without repeating characters efficiently (as removing a character from the front of a string isn't O(1)), we optimize the solution using a deque approach.
+ *
+ * Approach:
+ * 1) Initialize an unordered_map to track the frequency of characters.
+ * 2) Use a deque for pushing characters, and update the result deque (`res`) with the current deque (`temp`) 
+ *    whenever we find a longer substring.
+ * 3) Use a while loop to reduce the frequency from the front, incrementing `i`, 
+ *    and removing characters from the `temp` deque as we no longer need them.
+ * 4) Return `res.size()` as we are interested in the length of the longest substring.
+ * 
+ * Time Complexity: O(N)
+ * Space Complexity: O(N)
+ * 
+ * I hope this helps to understand.
+ * Thank you!
+ * @author [Ashish Kumar Sahoo](github.com/ashish5kmax)
+ **/
+
+#include <iostream>        // for IO Operations
+#include <unordered_map>   // for std::unordered_map
+#include <deque>           // for std::deque
+#include <string>          // for string class/string datatype which is taken as input
+#include <cassert>         // for assert
+
+/**
+ * @class Longest_Substring
+ * @brief Class that solves the Longest Substring Without Repeating Characters problem.
+ */
+class Longest_Substring {
+public:
+    /**
+     * @brief Function to find the length of the longest substring without repeating characters.
+     * @param s Input string.
+     * @return Length of the longest substring.
+     */
+    int lengthOfLongestSubstring(std::string s) {
+        // If the size of string is 1, then it will be the answer.
+        if (s.size() == 1) return 1;
+
+        // Map used to store the character frequency.
+        std::unordered_map<char, int> m;
+        int n = s.length();
+
+        // Deque to remove from back if repeating characters are present.
+        std::deque<char> temp;
+        std::deque<char> res;
+        int i, j;
+
+        // Sliding window approach using two pointers.
+        for (i = 0, j = 0; i < n && j < n;) {
+            m[s[j]]++;
+
+            // If repeating character found, update result and remove from the front.
+            if (m[s[j]] > 1) {
+                if (temp.size() > res.size()) {
+                    res = temp;
+                }
+
+                while (m[s[j]] > 1) {
+                    temp.pop_front();
+                    m[s[i]]--;
+                    i++;
+                }
+            }
+
+            // Add the current character to the deque.
+            temp.push_back(s[j]);
+            j++;
+        }
+
+        // Final check to update result.
+        if (temp.size() > res.size()) {
+            res = temp;
+        }
+
+        return res.size();  // Return the length of the longest substring.
+    }
+};
+
+/**
+ * @brief Self-test implementations
+ * @returns void
+ */
+static void tests() {
+    Longest_Substring soln;
+    assert(soln.lengthOfLongestSubstring("abcabcbb") == 3);
+    assert(soln.lengthOfLongestSubstring("bbbbb") == 1);
+    assert(soln.lengthOfLongestSubstring("pwwkew") == 3);
+    assert(soln.lengthOfLongestSubstring("") == 0); // Test case for empty string
+    assert(soln.lengthOfLongestSubstring("abcdef") == 6); // Test case for all unique characters
+    assert(soln.lengthOfLongestSubstring("a") == 1); // Single character
+    std::cout << "All test cases passed!" << std::endl;
+}
+
+/**
+ * @brief Main function.
+ * @return 0 on successful execution.
+ */
+int main() {
+    tests(); // run self-test implementations
+    return 0;
+}