[Leetcode] Longest Palindromic Substring

標籤：

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

最長迴文，對於每一個字元從中間向兩邊找，注意分奇數與偶數兩種情況。總的時間複雜度為O(n^2)。另外Manacher演算法複雜度為O(n)，Manacher演算法好複雜的樣子，智商捉急，得好好消化一下。先貼個簡單的吧。

 1 class Solution { 2 public: 3     int getLPS(const string &s, int idx1, int idx2) { 4         while (idx1 >= 0 && idx2 < s.length() && s[idx1] == s[idx2]) { 5             --idx1; 6             ++idx2; 7         } 8         return idx2 - idx1 - 1; 9     }10     11     string longestPalindrome(string s) {12         if (s.length() < 2) return s;13         int lps = -1, lps1, lps2, pos;14         for (int i = 0; i < s.length(); ++i) {15             lps1 = getLPS(s, i, i);16             lps2 = getLPS(s, i, i + 1);17             if (lps1 > lps || lps2 > lps) {18                 pos = i;19                 lps = max(lps1, lps2);20             }21         }22         if (lps & 0x1) return s.substr(pos-(lps-1)/2, lps);23         else return s.substr(pos-(lps-2)/2, lps);24     }25 };

 

[Leetcode] Longest Palindromic Substring