From 23a99c859d17d3b6516832420395dcacdd70282e Mon Sep 17 00:00:00 2001
From: Shreyash Kashyap <76607993+SYK-08@users.noreply.github.com>
Date: Mon, 2 Oct 2023 10:48:50 +0530
Subject: [PATCH] Create knuth_morris_pratt_algorithm.py

---
 searches/knuth_morris_pratt_algorithm.py | 70 ++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 searches/knuth_morris_pratt_algorithm.py

diff --git a/searches/knuth_morris_pratt_algorithm.py b/searches/knuth_morris_pratt_algorithm.py
new file mode 100644
index 000000000..1648821b1
--- /dev/null
+++ b/searches/knuth_morris_pratt_algorithm.py
@@ -0,0 +1,70 @@
+# https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm
+
+def knuth_morris_pratt(text: str, pattern: str) -> list[int]:
+    """
+    Knuth-Morris-Pratt (KMP) string search algorithm in Python.
+
+    :param text: The text in which to search for the pattern.
+    :param pattern: The pattern to search for in the text.
+    :return: A list of starting positions where the pattern is found in the text.
+
+    Examples:
+    >>> knuth_morris_pratt("ABABDABACDABABCABAB", "ABABCABAB")
+    [10]
+    >>> knuth_morris_pratt("ABCABCABCABCABC", "ABC")
+    [0, 3, 6, 9, 12]
+    >>> knuth_morris_pratt("AAAAAA", "AA")
+    [0, 1, 2, 3, 4]
+    >>> knuth_morris_pratt("ABCDEF", "XYZ")
+    []
+
+    """
+    def build_prefix_table(pattern: str) -> list[int]:
+        """
+        Build the prefix table for the given pattern.
+
+        :param pattern: The pattern for which to build the prefix table.
+        :return: The prefix table, which is a list of integers.
+
+        Examples:
+        >>> build_prefix_table("ABABCA")
+        [0, 0, 1, 2, 3, 0]
+        >>> build_prefix_table("ABCABC")
+        [0, 0, 0, 1, 2, 3]
+        >>> build_prefix_table("AAAAAA")
+        [0, 1, 2, 3, 4, 5]
+        >>> build_prefix_table("XYZ")
+        [0, 0, 0]
+
+        """
+        prefix_table = [0] * len(pattern)
+        j = 0
+        for i in range(1, len(pattern)):
+            while j > 0 and pattern[i] != pattern[j]:
+                j = prefix_table[j - 1]
+            if pattern[i] == pattern[j]:
+                j += 1
+            prefix_table[i] = j
+        return prefix_table
+
+    prefix_table = build_prefix_table(pattern)
+    positions = []
+    j = 0
+    for i in range(len(text)):
+        while j > 0 and text[i] != pattern[j]:
+            j = prefix_table[j - 1]
+        if text[i] == pattern[j]:
+            j += 1
+        if j == len(pattern):
+            positions.append(i - j + 1)
+            j = prefix_table[j - 1]
+    return positions
+
+if __name__ == "__main__":
+    text = input("Enter the text: ")
+    pattern = input("Enter the pattern to search for: ")
+    positions = knuth_morris_pratt(text, pattern)
+    if positions:
+        print(f"Pattern found at positions: {positions}")
+    else:
+        print("Pattern not found in the text.")