回文子串数量

中心扩展算法

import java.util.*;


public class Solution {
  /**
   * 
   * @param str string字符串 
   * @return int整型
   */
  public int palindromeCount (String str) {
    int ans = 0;
    for (int center = 0; center < str.length(); center++) {
      ans += expand(str, center, center) + expand(str, center, center + 1);
    }
    return ans;
  }

  private int expand(String str, int left, int right) {
    int ans = 0;
    while (left >= 0 && right < str.length() && str.charAt(left) == str.charAt(right)) {
      ans++;
      left--;
      right++;
    }
    return ans;
  }
}