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Author: lmizner

Sliding_Windows/longest_nonrepeating_substring.py

@@ -0,0 +1,60 @@
+def find_longest_substring(input_str):
+    # Check the length of input_str
+    if len(input_str) == 0:
+        return 0
+
+    window_start, longest, window_length = 0, 0, 0
+
+    last_seen_at = {}
+
+    # Traverse str to find the longest substring 
+    # without repeating characters.
+    for index, val in enumerate(input_str):
+        # If the current element is not present in the hash map,
+        # then store it in the hash map with the current index as the value.
+        if val not in last_seen_at:
+            last_seen_at[val] = index
+        else:
+            # If the current element is present in the hash map,
+            # it means that this element may have appeared before.
+            # Check if the current element occurs before or after `window_start`.
+            if last_seen_at[val] >= window_start:
+                window_length = index - window_start
+                if longest < window_length:
+                    longest = window_length
+                window_start = last_seen_at[val] + 1
+
+            # Update the last occurrence of
+            # the element in the hash map
+            last_seen_at[val] = index
+
+    index += 1
+    # Update the longest substring's
+    # length and starting index.
+    if longest < index - window_start:
+        longest = index - window_start
+
+    return longest
+
+
+# Driver code
+def main():
+    string = [
+        "abcabcbb",
+        "pwwkew",
+        "bbbbb",
+        "ababababa",
+        "",
+        "ABCDEFGHI",
+        "ABCDEDCBA",
+        "AAAABBBBCCCCDDDD",
+    ]
+    for i in range(len(string)):
+        print(i + 1, ". \t Input String: ", string[i], sep="")
+        print("\t Length of longest substring: ",
+                (find_longest_substring(string[i])))
+        print("-" * 100)
+
+
+if __name__ == "__main__":
+    main()

Sliding_Windows/minimum_window_substring.py

@@ -0,0 +1,69 @@
+def min_window(s, t):
+    # empty string scenario
+    if t == "":
+        return ""
+    
+    # creating the two hash maps
+    req_count = {}
+    window = {}
+
+    # populating req_count hash map
+    for c in t:
+        req_count[c] = 1 + req_count.get(c, 0)
+
+    # populating window hash map
+    for c in t:
+        window[c] = 0
+
+    # setting up the conditional variables
+    current, required = 0, len(req_count)
+    
+    # setting up a variable containing the result's starting and ending point
+    # with default values and a length variable
+    res, res_len = [-1, -1], float("infinity")
+    
+    # setting up the sliding window pointers
+    left = 0
+    for right in range(len(s)):
+        c = s[right]
+
+        # if the current character also occurs in t, update its frequency in window hash map
+        if c in t:
+            window[c] = 1 + window.get(c, 0)
+
+        # updating the current variable
+        if c in req_count and window[c] == req_count[c]:
+            current += 1
+
+        # adjusting the sliding window
+        while current == required:
+            # update our result
+            if (right - left + 1) < res_len:
+                res = [left, right]
+                res_len = (right - left + 1)
+            
+            # pop from the left of our window
+            if s[left] in t:
+                window[s[left]] -= 1
+
+            # if the popped character was among the required characters and
+            # removing it has reduced its frequency below its frequency in t, decrement current
+            if s[left] in req_count and window[s[left]] < req_count[s[left]]:
+                current -= 1
+            left += 1
+    left, right = res
+
+    # return the minimum window substring
+    return s[left:right+1] if res_len != float("infinity") else ""
+
+# driver Code
+def main():
+    s = ["PATTERN", "LIFE", "ABRACADABRA", "STRIKER", "DFFDFDFVD"]
+    t = ["TN", "I", "ABC", "RK", "VDD"]
+    for i in range(len(s)):
+        print(i + 1, ".\ts: ", s[i], "\n\tt: ", t[i], "\n\tThe minimum substring containing ", \
+              t[i], " is: ", min_window(s[i], t[i]), sep="")
+        print("-" * 100)
+
+if __name__ == '__main__':
+    main()