solve 647.palindromic-substrings

Author: andavid

vscode/647.palindromic-substrings.java

@@ -0,0 +1,72 @@
+/*
+ * @lc app=leetcode id=647 lang=java
+ *
+ * [647] Palindromic Substrings
+ *
+ * https://leetcode.com/problems/palindromic-substrings/description/
+ *
+ * algorithms
+ * Medium (57.70%)
+ * Likes:    1608
+ * Dislikes: 82
+ * Total Accepted:    116.8K
+ * Total Submissions: 202K
+ * Testcase Example:  '"abc"'
+ *
+ * Given a string, your task is to count how many palindromic substrings in
+ * this string.
+ *
+ * The substrings with different start indexes or end indexes are counted as
+ * different substrings even they consist of same characters.
+ *
+ * Example 1:
+ *
+ *
+ * Input: "abc"
+ * Output: 3
+ * Explanation: Three palindromic strings: "a", "b", "c".
+ *
+ *
+ *
+ *
+ * Example 2:
+ *
+ *
+ * Input: "aaa"
+ * Output: 6
+ * Explanation: Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa".
+ *
+ *
+ *
+ *
+ * Note:
+ *
+ *
+ * The input string length won't exceed 1000.
+ *
+ *
+ *
+ *
+ */
+class Solution {
+  public int countSubstrings(String s) {
+    int count = 0;
+    for (int i = 0; i < s.length(); i++) {
+      count += palindromic(s, i, i);
+      count += palindromic(s, i, i + 1);
+    }
+    return count;
+  }
+
+  public int palindromic(String s, int left, int right) {
+    int count = 0;
+    while (left >= 0 && right < s.length()
+      && (s.charAt(left) == s.charAt(right))) {
+      left--;
+      right++;
+      count++;
+    }
+    return count;
+  }
+}
+