Create 647.Palindromic-Substrings_v2.cpp

Author: wisdompeak

String/647.Palindromic-Substrings/647.Palindromic-Substrings_v2.cpp

@@ -0,0 +1,47 @@
+class Solution {
+public:
+    int countSubstrings(string s) 
+    {
+        string t = "#";
+        for (auto ch: s)
+        {
+            t.push_back(ch);
+            t.push_back('#');
+        }
+        
+        int n = t.size();
+        vector<int>P(n);
+        int maxCenter = -1;
+        int maxRight = -1;
+        for (int i=0; i<n; i++)
+        {
+            int r;
+            if (i <= maxRight)
+            {
+                int j = maxCenter*2-i;
+                r = min(P[j], maxRight-i);
+                while (i-r>=0 && i+r<n && t[i-r]==t[i+r])
+                    r++;                
+            }
+            else
+            {
+                r = 0;
+                while (i-r>=0 && i+r<n && t[i-r]==t[i+r])
+                    r++;  
+            }
+            P[i] = r-1;
+            if (i+P[i]>maxRight)
+            {
+                maxRight = i+P[i];
+                maxCenter = i;
+            }
+        }
+        
+        int ret = 0;
+        for (int i=0; i<n; i++)
+        {
+            ret += (P[i]+1)/2;
+        }
+        return ret;
+    }
+};