leetcode-中心扩散法-回文数

/**
 * <p>给你一个字符串 <code>s</code>，找到 <code>s</code> 中最长的回文子串。</p>
 *
 * <p>&nbsp;</p>
 *
 * <p><strong>示例 1：</strong></p>
 *
 * <pre>
 * <strong>输入：</strong>s = "babad"
 * <strong>输出：</strong>"bab"
 * <strong>解释：</strong>"aba" 同样是符合题意的答案。
 * </pre>
 *
 * <p><strong>示例 2：</strong></p>
 *
 * <pre>
 * <strong>输入：</strong>s = "cbbd"
 * <strong>输出：</strong>"bb"
 * </pre>
 *
 * <p>&nbsp;</p>
 *
 * <p><strong>提示：</strong></p>
 *
 * <ul>
 * <li><code>1 &lt;= s.length &lt;= 1000</code></li>
 * <li><code>s</code> 仅由数字和英文字母组成</li>
 * </ul>
 * <div><div>Related Topics</div><div><li>字符串</li><li>动态规划</li></div></div><br><div><li>👍 5640</li><li>👎 0</li></div>
 */

//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    //中心扩散法
    public String longestPalindrome(String s) {
        int strLen = s.length();
        int left = 0;
        int right = 0;
        int len = 1;
        int maxStart = 0;
        int maxLen = 0;

        for (int i = 0; i < strLen; i++) {
            left = i - 1;
            right = i + 1;
            while (left >= 0 && s.charAt(left) == s.charAt(i)) {
                len++;
                left--;
            }
            while (right < strLen && s.charAt(right) == s.charAt(i)) {
                len++;
                right++;
            }
            while (left >= 0 && right < strLen && s.charAt(left) == s.charAt(right)) {
                len += 2;
                left--;
                right++;
            }
            if (len > maxLen) {
                maxLen = len;
                maxStart = left;
            }
            len = 1;
        }
        return s.substring(maxStart + 1, maxStart + maxLen + 1);
    }
}
//leetcode submit region end(Prohibit modification and deletion)