回文串的马拉车算法

Author: uwivbn

5. 最长回文子串/file_code3.py

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+class Solution:
+    # 马拉车算法
+    def longestPalindrome(self, s: str) -> str:
+        T = preprocess(s)
+        n = len(T)
+        C, R = 0, 0
+        P = [0] * n
+
+        for i in range(1, n-1):
+            i_mirror = 2 * C - i
+            P[i] = min(R-i, P[i_mirror]) if R > i else 0
+
+            while T[i-1-P[i]] == T[i+1+P[i]]:
+                P[i] += 1
+
+            if i + P[i] > R:
+                C = i
+                R = P[i] + i
+
+        maxlen = 0
+        center_index = 0
+        for i in range(1, n-1):
+            if P[i] > maxlen:
+                maxlen = P[i]
+                center_index = i
+
+        start_index = (center_index - maxlen) // 2
+        return s[start_index: maxlen + start_index]
+
+
+def preprocess(s: str):
+    temp_str = ''
+    for i in s:
+        temp_str += '#' + i
+
+    temp_str = '^' + temp_str + '#$'
+    return temp_str
+
+if __name__ == "__main__":
+    solution = Solution()
+    # string = 'cbbd'
+    string = 'babad'
+
+    result = solution.longestPalindrome(string)
+
+    print(result)