最长回文字串

import java.util.Arrays;

public class test200
{
	
	public static void main(String[] args)
	{
		String s="xabbac";
		int a=longestPalindrome(s);
		System.out.println();
	}
	
	public static int longestPalindrome(String s)
	{
		char[] carr=s.toCharArray();
		int[][] dp=new int[carr.length][carr.length];
		for(int i=0;i<carr.length;i++)
			Arrays.fill(dp[i], -1);
		return dp(0, carr.length-1, carr,dp);
		
	}
	
	
	public static int dp(int a,int b,char[] carr,int[][] dp)
	{
		if(dp[a][b]>-1)
			return dp[a][b];
		if(a==b)
			return dp[a][b]=1; // "aba" <- "a"
		if(a>b)
			return dp[a][b]=0; // "bb"  <- ""
		
		if(carr[a]==carr[b])
			if(check(a+1, b-1, carr))
				return dp[a][b]=dp(a+1, b-1, carr,dp)+2;
		
		return dp[a][b]=Math.max(dp(a+1, b, carr,dp),dp(a, b-1, carr,dp));
	}
	
	public static boolean check(int a,int b,char[] carr)
	{
		if(a>=b)
			return true;
		if(carr[a]!=carr[b])
			return false;
		
		return check(a+1, b-1, carr);
	}
}

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输出串

import java.util.Arrays;

public class test200
{
	
	public static void main(String[] args)
	{
		String s="ababbababauiopjsjsjsjsjsjx";
		String ss=longestPalindrome(s);
		System.out.println(ss);
	}
	
	public static String longestPalindrome(String s)
	{
		char[] carr=s.toCharArray();
		int[][] dp=new int[carr.length][carr.length];
		int[][] start=new int[carr.length][carr.length];
		for(int i=0;i<carr.length;i++)
			Arrays.fill(dp[i], -1);
		
		int len=dp(0, carr.length-1, carr,dp,start);
		String ss=s.substring(start[0][carr.length-1], start[0][carr.length-1]+len);
		return ss;
		
	}
	
	
	public static int dp(int a,int b,char[] carr,int[][] dp,int[][] start)
	{
		if(dp[a][b]>-1)
			return dp[a][b];
		if(a==b)
		{
			start[a][b]=a;
			return dp[a][b]=1;
		}
		if(a>b)
		{
			start[a][b]=a;
			return dp[a][b]=0;
		}
		
		if(carr[a]==carr[b])
			if(check(a+1, b-1, carr))
			{
				start[a][b]=a;
				return dp[a][b]=dp(a+1, b-1, carr,dp,start)+2;
			}
		
		int m=dp(a+1, b, carr,dp,start);
		int n=dp(a, b-1, carr,dp,start);
		int ret=m;
		if(m>n)
			start[a][b]=start[a+1][b];
		else {
			start[a][b]=start[a][b-1];
			ret=n;
		}
		
		return dp[a][b]=ret;
	}
	
	public static boolean check(int a,int b,char[] carr)
	{
		if(a>=b)
			return true;
		if(carr[a]!=carr[b])
			return false;
		
		return check(a+1, b-1, carr);
	}
}