Longest palindromic substring.

Author: recherst

Medium/5.Longest Palindromic Substring.playground/Contents.swift

@@ -0,0 +1,54 @@
+/**
+ Given a string s, return the longest palindromic substring in s.
+
+  
+
+ Example 1:
+ Input: s = "babad"
+ Output: "bab"
+ Explanation: "aba" is also a valid answer.
+ 
+ Example 2:
+ Input: s = "cbbd"
+ Output: "bb"
+  
+
+ Constraints:
+ - 1 <= s.length <= 1000
+ - s consist of only digits and English letters.
+ */
+class Solution {
+    private var leftPosition = 0
+    private var rightPosition = 0
+    private var maxLength = 0
+    func longestPalindrome(_ s: String) -> String {
+        let characterArr = s.map { $0 }
+        for i in 0..<s.count {
+            var index1 = i
+            var index2 = i
+            findPalindrome(characterArr, leftPosition: &index1, rightPosition: &index2)
+            var index3 = i
+            var index4 = i + 1
+            findPalindrome(characterArr, leftPosition: &index3, rightPosition: &index4)
+        }
+        return String(s[s.index(s.startIndex, offsetBy: leftPosition)...s.index(s.startIndex, offsetBy: rightPosition)])
+    }
+    
+    private func findPalindrome(_ s: [Character], leftPosition left: inout Int, rightPosition right: inout Int) {
+        let n = s.count
+        while left >= 0 && right < n && s[left] == s[right] {
+            if right - left + 1 > maxLength {
+                leftPosition = left
+                rightPosition = right
+                maxLength = right - left + 1
+            }
+            left -= 1
+            right += 1
+        }
+    }
+}
+
+let s = Solution()
+let r = s.longestPalindrome(
+    "lphbehiapswjudnbcossedgioawodnwdruaaxhbkwrxyzaxygmnjgwysafuqbmtzwdkihbwkrjefrsgjbrycembzzlwhxneiijgzidhngbmxwkhphoctpilgooitqbpjxhwrekiqupmlcvawaiposqttsdgzcsjqrmlgyvkkipfigttahljdhtksrozehkzgshekeaxezrswvtinyouomqybqsrtegwwqhqivgnyehpzrhgzckpnnpvajqevbzeksvbezoqygjtdouecnhpjibmsgmcqcgxwzlzztdneahixxhwwuehfsiqghgeunpxgvavqbqrelnvhnnyqnjqfysfltclzeoaletjfzskzvcdwhlbmwbdkxnyqappjzwlowslwcbbmcxoiqkjaqqwvkybimebapkorhfdzntodhpbhgmsspgkbetmgkqlolsltpulgsmyapgjeswazvhxedqsypejwuzlvegtusjcsoenrcmypexkjxyduohlvkhwbrtzjnarusbouwamazzejhnetfqbidalfomecehfmzqkhndpkxinzkpxvhwargbwvaeqbzdhxzmmeeozxxtzpylohvdwoqocvutcelgdsnmubyeeeufdaoznxpvdiwnkjliqtgcmvhilndcdelpnilszzerdcuokyhcxjuedjielvngarsgxkemvhlzuprywlypxeezaxoqfges")
+print(r)

Medium/5.Longest Palindromic Substring.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios' buildActiveScheme='true' importAppTypes='true'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Medium/5.Longest Palindromic Substring.playground/playground.xcworkspace/contents.xcworkspacedata

@@ -107,3 +107,4 @@
 
 1. [Min Stack](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/155.Min%20Stack.playground/Contents.swift)
 2. [Longest Substring Without Repeating Characters](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/3.Longest%20Substring%20Without%20Repeating%20Characters.playground/Contents.swift)
+3. [Longest Palindromic Substring](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/5.Longest%20Palindromic%20Substring.playground/Contents.swift)