回文串的中心匹配

5. 最长回文子串/file_code2.py

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+class Solution:
+    # 中心匹配
+    def longestPalindrome(self, s: str) -> str:
+        if s == '' and s is None:
+            return ''
+        start, end = 0, 0
+        for i in range(len(s)):
+            len1 = expendstr(s, i, i)
+            len2 = expendstr(s, i, i+1)
+            maxlen = max(len1, len2)
+            # print(len1, len2)
+            if maxlen > end - start:
+                start = i - (maxlen-1)//2
+                end = i + maxlen // 2 + 1
+                # print(maxlen, start, end)
+
+        return s[start: end]
+
+
+def expendstr(s: str, left: int, right: int):
+    L, R = left, right
+    while L >= 0 and R < len(s) and s[L] == s[R]:
+        L, R = L - 1, R + 1
+
+    return R - L - 1
+
+
+if __name__ == "__main__":
+    solution = Solution()
+    # string = 'cbbd'
+    string = 'a'
+
+    # print(expendstr('abba', 1, 2))
+    result = solution.longestPalindrome(string)
+
+    print(result)