palindromic substrings solution

Author: yhkee0404

palindromic-substrings/yhkee0404.go

@@ -0,0 +1,38 @@
+func countSubstrings(s string) int {
+    runes := []rune{} // S(n) = O(n)
+    for _, c := range s {
+        runes = append(runes, c)
+        runes = append(runes, '\000')
+    }
+    ans := 0
+    dp := make([]int, len(runes) - 1)
+    lastR := -1
+    lastMid := -1
+    i := 0
+    for i != len(dp) { // Manacher T(n) = O(n)
+        diff := lastR - i
+        deviation := 0
+        if diff > 0 {
+            deviation = min(diff, dp[lastMid - (i - lastMid)])
+        }
+        l := i - deviation
+        r := i + deviation
+        for l != 0 && r + 1 != len(dp) && runes[l - 1] == runes[r + 1] {
+            deviation++
+            l--
+            r++
+        }
+        dp[i] = deviation
+        if r > lastR {
+            lastR = r
+            lastMid = i
+        }
+        if runes[i] == '\000' {
+            ans += (deviation + 1) >> 1
+        } else {
+            ans += 1 + (deviation >> 1)
+        }
+        i++
+    }
+    return ans
+}