feat: Add num of ways to split string algorithm

dynamic_programming/decode_ways.py

@@ -0,0 +1,47 @@
+"""
+A message containing letters from A-Z is being encoded to numbers using the
+following mapping:
+'A' -> 1
+'B' -> 2
+...
+'Z' -> 26
+Given a non-empty string containing only digits,
+determine the total number of ways to decode it.
+"""
+
+def num_decodings(s: str):
+    """
+    >> num_decodings("12")
+    2
+    >> num_decodings("226")
+    3
+    """
+    if not s or int(s[0]) == 0:
+        return 0
+
+    last = 1
+    second_last = 1
+
+    for i in range(1, len(s)):
+        # 0 is a special digit since it does not
+        # correspond to any alphabet but can be
+        # meaningful if preceeded by 1 or 2
+
+        if s[i] == "0":
+            if s[i-1] in {"1", "2"}:
+                curr = second_last
+            else:
+                return 0
+        elif 11 <= int(s[i-1:i+1]) <= 26:
+            curr = second_last + last
+        else:
+            curr = last
+
+        last, second_last = curr, last
+    return last
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()

strings/num_splits.py

@@ -0,0 +1,44 @@
+"""
+You are given a string s, a split is called good if you can split s into
+2 non-empty strings p and q where its concatenation is equal to s and
+the number of distinct letters in p and q are the same.
+
+Return the number of good splits you can make in s. 
+"""
+from collections import Counter, defaultdict
+
+def num_splits(self, s: str):
+        """
+        >> num_splits("aacaba")
+        2
+        >> num_splits("abcd")
+        1
+        >> num_splits("aaaaa")
+        4
+        """
+        ans = 0
+        rightSplit = Counter(s)
+        leftSplit = defaultdict(int)
+
+        leftCount = 0
+        rightCount = len(rightSplit)
+
+        for ch in s:
+            rightSplit[ch] -= 1
+            leftSplit[ch] += 1
+
+            if rightSplit[ch] == 0:
+                rightCount -= 1
+
+            leftCount = len(leftSplit)
+
+            if leftCount == rightCount:
+                ans += 1
+
+        return ans
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()