From c6760f0a68b4fa4b7eecc79ffab48f047fd7e556 Mon Sep 17 00:00:00 2001
From: ehlxr <ehlxr.me@gmail.com>
Date: Sat, 4 Jun 2022 14:34:28 +0800
Subject: [PATCH] longestPalindrome

---
 main.go           | 30 ++++++++++++++++++------------
 src/palindrome.go | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 12 deletions(-)
 create mode 100644 src/palindrome.go

diff --git a/main.go b/main.go
index 0e07505..70385bc 100644
--- a/main.go
+++ b/main.go
@@ -1,22 +1,28 @@
 package main
 
 import (
-	"fmt"
-
 	. "github.com/ehlxr/leetcode-go/src"
 )
 
 func main() {
-	node5 := &ListNode{Val: 5, Next: nil}
-	node4 := &ListNode{Val: 4, Next: node5}
-	node3 := &ListNode{Val: 3, Next: node4}
-	node2 := &ListNode{Val: 2, Next: node3}
-	node1 := &ListNode{Val: 1, Next: node2}
-	root := &ListNode{Val: 0, Next: node1}
-
-	fmt.Printf("%v\n", root)
-
+	// node5 := &ListNode{Val: 5, Next: nil}
+	// node4 := &ListNode{Val: 4, Next: node5}
+	// node3 := &ListNode{Val: 3, Next: node4}
+	// node2 := &ListNode{Val: 2, Next: node3}
+	// node1 := &ListNode{Val: 1, Next: node2}
+	// root := &ListNode{Val: 0, Next: node1}
+	// fmt.Printf("%v\n", root)
+	//
 	// fmt.Printf("%v\n", Reverse(root))
-	fmt.Printf("%v\n", ReverseRec(root))
+	// fmt.Printf("%v\n", ReverseRec(root))
 	// fmt.Printf("%v\n", ReverseKGroup(root, 2))
+
+	// s := "Hello 你好"
+	// println(s[2], s[6])
+	// rs := []rune(s)
+	// println(string(rs[6]))
+
+	s := "babad"
+	println(LongestPalindrome(s))
+
 }
diff --git a/src/palindrome.go b/src/palindrome.go
new file mode 100644
index 0000000..b647ce3
--- /dev/null
+++ b/src/palindrome.go
@@ -0,0 +1,33 @@
+package src
+
+/* 给你一个字符串 s，找到 s 中最长的回文子串 */
+func LongestPalindrome(s string) string {
+	var res string
+	for i := 0; i < len(s); i++ {
+		// 回文串长度为奇数
+		p1 := palindrome(s, i, i)
+		if len(p1) > len(res) {
+			res = p1
+		}
+
+		// 回文串长度为偶数
+		p2 := palindrome(s, i, i+1)
+		if len(p2) > len(res) {
+			res = p2
+		}
+	}
+
+	return res
+}
+
+// 从中心向两段扩展
+func palindrome(s string, l, r int) string {
+	for l >= 0 && r < len(s) && s[l] == s[r] {
+		l--
+		r++
+	}
+
+	// (r-1)-l 为回文串的长度
+	// s[l+1 : (r-1)-l+(l+1)] 为回文串
+	return s[l+1 : r]
+}