leetcode: Add 0005 solution

src/leetcode/0005.longest-palindromic-substring/main.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+
+def longestPalindrome(s: str) -> str:
+    # 跟据回文字符串的特性
+
+    def twoSidesEqual(s: str, left: int, right: int) -> bool:
+        # 先检查两个索引值的有效性, 再比较它们指向的字符是否相等.
+        if left >= 0 and right < len(s) and s[left] == s[right]:
+            return True
+        else:
+            return False
+
+    longest_palindrome_len = 0
+    longest_palindrome_start = 0
+
+    # 遍历所有字符
+    for middle in range(len(s)):
+        # 以 (middle) 为对称点, substring 有奇数个字符
+        left = middle
+        right = middle
+        while twoSidesEqual(s, left, right):
+            length = right - left + 1
+            if longest_palindrome_len < length
+                longest_palindrome_len = length
+                longest_palindrome_start = left
+            left -= 1
+            right += 1
+
+        # 以 (middle, middle+1) 作为对称点, substring 有偶数个字符
+        left = middle
+        right = middle + 1
+        while twoSidesEqual(s, left, right):
+            length = right - left + 1
+            if longest_palindrome_len < length
+                longest_palindrome_len = length
+                longest_palindrome_start = left
+            left -= 1
+            right += 1
+
+    # 返回结果
+    return s[longest_palindrome_start:longest_palindrome_start+longest_palindrome_len]
+
+def main():
+    s1 = "babad"
+    out1 = longestPalindrome(s1)
+    assert(out1 == "bab")
+
+    s2 = "cbbd"
+    out2 = longestPalindrome(s2)
+    assert(out2 == "bb")
+
+if __name__ == "__main__":
+    main()