[Leetcode series] Longest reply string Problem

Given the string S, find the longest input string in its substring.

Inversion Method: If S is reversed, find the longest common substring S, and check whether the subscript of S in S is satisfied with the subscript is in S: length (S) = is + is '+ Length (s ). if yes, S is the search result. If not, we will continue searching.

DP Solution: Define P [I] [J] = true <-> Si... SJ is the input string, otherwise false; P [I + 1] [J-1] = true & Si = SJ <-> P [I] [J] = true; basically, P [I] [I] = true and P [I] [I + 1] = (SI = Si + 1) so that we can construct and search within the Square time, and use the square space.

 1 class Solution { 2 public: 3     string longestPalindrome(string s) { 4         if (s.length() <= 1) return s; 5         // DP solution 6         bool P[1000][1000] = {false}; 7         int start = 0; 8         int maxLen = 0; 9         for (int i = 0; i < s.length(); i++) {10             P[i][i] = true;11         }12         for (int i = 0; i < s.length() - 1; i++) {13             if (s[i] == s[i+1]) {14                 P[i][i+1] = true;15                 start = i;16                 maxLen = 2;17             }18         }19         for (int len = 3; len <= s.length(); len++) {20             for (int i = 0; i < s.length() - len + 1; i++) {21                 int j = i + len - 1;22                 if (s[j] == s[i] && P[i+1][j-1]) {23                     P[i][j] = true;24                     start = i;25                     maxLen = len;26                 }27             }28         }29         return s.substr(start, maxLen);30     }31 };

Center Method: A back-to-text is always centered on a specific character. The center contains 2n-1 (including "blank" in the middle of 2 characters "). considering that expansion from the center requires O (n) times, the total time complexity is O (n2 ).

 1 class Solution { 2 public: 3     string longestPalindrome(string s) { 4         if (s.length() <= 1) return s; 5         string longest = s.substr(0, 1); 6         // Center Solution 7         for (int i = 0; i < s.length() - 1; i++) { 8             string res = expandFromCenter(s, i, i); 9             if (res.length() > longest.length()) longest = res;10             res = expandFromCenter(s, i, i+1);11             if (res.length() > longest.length()) longest = res;12         }13         return longest;14     }15     16     string expandFromCenter(string s, int l, int r) {17         while (l >= 0 && r < s.length() && s[l] == s[r]) {18             l--;19             r++;20         }21         return s.substr(l+1, r-l-1);22     }23 };

 

Manacher method: Linear Time solution, complex, and timestamp.

[Leetcode series] Longest reply string Problem