Difficulty

Medium

Description

/**
 * Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.
 *
 * Example 1:
 * Input: "babad"
 * Output: "bab"
 * Note: "aba" is also a valid answer.
 * 
 * Example 2:
 * Input: "cbbd"
 * Output: "bb"
 */
 

Solution

class Solution {
    	public int len = 0;
    	public String str = "";
    	
    	public String longestPalindrome(String s) {
    		int n = s.length();
    		if (n == 0)
    			return "";
    		if (n == 1)
    			return s;
    		//分成奇數和偶數兩種情況
    		for (int i = 0; i < n; i++) {
    			sub
 
(s, i, i);
    		}
    		for (int i = 0; i < n - 1; i++) {
        		sub(s, i, i + 1);
        	}	
    	    return str;
    	}
    	
    	//利用短迴文繼續判斷長迴文
    	public void sub(String s, int i, int j) {
    		if (s.charAt(i) == s.charAt(j)) {
    			if (i > 0 && j < s.length()-1) {
    				sub
 
(s, i - 1, j + 1);
    			}
    			if (len < j - i + 1) {
    				len = j - i + 1;
    				str = s.substring(i, j + 1);
    			}
    		} 
    	}
    	
    }