Leetcode day 2 and 3

leetcode/lc5/brute.cpp

@@ -0,0 +1,23 @@
+class Solution{
+    public: 
+        string LongestPalindrome(string s){
+            for(int length= s.size();i>0;i--){
+                for(int start = 0;start<=s.size()-length;start++){
+                    if(check(s,start,start+length))
+                        return s.substr(start,length);
+                }
+            }
+        }
+            private: bool check(string s, int i, int j){
+                         int left = i;
+                         int right = j-1;
+                         while(left<right){
+                             if(s[left]!=S[right])
+                                 return false;
+                             left++;
+                             right--;
+                         }
+                         return true;
+                     }
+        
+};

leetcode/lc5/manachers.cpp

@@ -0,0 +1,41 @@
+class Solution{
+    public:
+        string LongestPalindrome(string s){
+            if(s.empty()) return "";
+            string t = "#";
+            for(char c : s){
+                t+=c;
+                t+="#";
+            }
+            int n = t.size();
+            vector<int> p(n,0);
+            int C =0;
+            int R =0;
+
+            for(int i=0;i<n;i++){
+                int mirror = 2*C-i;
+
+                if(i<R){
+                    p[i] = min(R-i, p[mirror]);
+                }
+                while(i+p[i]+1<n && i-p[i]-1>=0 && t[i+p[i]+1] == t[i-p[i]-1]){
+                            p[i]++;
+                }
+                if(i+p[i]>R){
+                C = i;
+                R = i+p[i];
+                }
+
+            }
+            int maxLen = 0;
+            int centerIndex = 0;
+            for(int i =0;i<n;i++){
+                if(p[i]>maxLen){
+                    maxLen = p[i];
+                    centerIndex = i;
+                }
+            }
+            int start = (centerIndex-maxLen)/2;
+            return s.substr(start, maxLen);
+        }
+}