feat(dp): palindrome partitioning - minimum cuts (O(n²))

dynamic_programming/better_palindrome_partitioning/palindrome_partitioning.py

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+"""Palindrome partitioning module.
+
+Given a string s, partition s such that every substring of the partition is a palindrome.
+Find the minimum cuts needed for a palindrome partitioning of s.
+
+Time complexity: O(n^2)
+Space complexity: O(n^2) [can be optimized to O(n)]
+"""
+
+from typing import List, Tuple, Union
+
+
+def find_minimum_partitions(
+    s: str, return_partitions: bool = False
+) -> Union[int, Tuple[int, List[str]]]:
+    """Return minimum cuts and optionally one valid partitioning."""
+    n = len(s)
+    if n <= 1 or s == s[::-1]:
+        return (0, [s]) if return_partitions else 0
+
+    # DP tables
+    cuts = [0] * n
+    is_palindrome = [[False] * n for _ in range(n)]
+    parent = [-1] * n  # tracks where to jump back for reconstruction
+
+    for i in range(n):
+        min_cuts = i
+        for j in range(i + 1):
+            if s[j] == s[i] and (i - j <= 1 or is_palindrome[j + 1][i - 1]):
+                is_palindrome[j][i] = True
+                if j == 0:
+                    min_cuts = 0
+                    parent[i] = -1
+                else:
+                    candidate = cuts[j - 1] + 1
+                    if candidate < min_cuts:
+                        min_cuts = candidate
+                        parent[i] = j - 1
+        cuts[i] = min_cuts
+
+    if not return_partitions:
+        return cuts[-1]
+
+    # Reconstruct one valid partitioning
+    partitions: List[str] = []
+    i = n - 1
+    while i >= 0:
+        start = parent[i] + 1 if parent[i] != -1 else 0
+        partitions.append(s[start : i + 1])
+        if parent[i] == -1:
+            break
+        i = parent[i]
+
+    partitions.reverse()
+    return (cuts[-1], partitions)
+
+
+if __name__ == "__main__":
+    s = input("enter the string:").strip()
+    cuts, partitions = find_minimum_partitions(s, return_partitions=True)
+    print(f"Minimum cuts required: {cuts}")
+    print("One possible palindrome partitioning:")
+    print(" | ".join(partitions))