From 95f023f12a7fd3d0a6a649a0f1aaa348ebc19b9f Mon Sep 17 00:00:00 2001
From: SquidSpirit <squid@squidspirit.com>
Date: Thu, 13 Feb 2025 23:08:55 +0800
Subject: [PATCH] feat: 5_longest_palindromic_substring

---
 5_longest_palindromic_substring/main.cpp | 59 ++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 5_longest_palindromic_substring/main.cpp

diff --git a/5_longest_palindromic_substring/main.cpp b/5_longest_palindromic_substring/main.cpp
new file mode 100644
index 0000000..6fa16a3
--- /dev/null
+++ b/5_longest_palindromic_substring/main.cpp
@@ -0,0 +1,59 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+public:
+    int findPalindromeLength(const string &str, int center, int skip) {
+        for (int radius = skip; center - radius >= 0 && center + radius < str.length(); radius++) {
+            char r = str[center + radius];
+            char l = str[center - radius];
+
+            if (r != l) {
+                return radius - 1;
+            }
+        }
+
+        return min(center, (int)str.length() - 1 - center);
+    }
+
+    string longestPalindrome(string s) {
+        string str = "#";
+        for (auto c : s) {
+            str.push_back(c);
+            str.push_back('#');
+        }
+
+        vector<int> p(str.length(), 0);
+        int center = 0, right = 0, maxRadius = 0;
+        for (int index = 1; index < str.length() - 1; index++) {
+            if (index > right) {
+                int radius = findPalindromeLength(str, index, 1);
+                p[index] = radius;
+                if (radius >= maxRadius) {
+                    maxRadius = radius;
+                    center = index;
+                    right = center + radius;
+                }
+                continue;
+            }
+
+            int indexMirror = center - (index - center);
+            if (index + p[indexMirror] < right) {
+                p[index] = p[indexMirror];
+                continue;
+            }
+
+            int radius = findPalindromeLength(str, index, right - index);
+            p[index] = radius;
+            if (radius >= maxRadius) {
+                maxRadius = radius;
+                center = index;
+                right = center + radius;
+            }
+        }
+
+        int start = (center - maxRadius) / 2;
+        int length = maxRadius;
+        return s.substr(start, length);
+    }
+};