给你一个字符串 s，找到 s 中最长的回文子串。

#include<string.h>
#include<stdio.h>
#define N 20
int main()
{
	char S[N]="\0";
    int dp[N][N];
	gets(S);
	int len = strlen(S), ans = 1;
	memset(dp, 0, sizeof(dp));
	for (int i = 0; i < len; i++)
	{
		dp[i][i] = 1;
		if (i < len - 1)
		{
			if (S[i] == S[i + 1])
			{
				dp[i][i + 1] = 1;
				ans = 2;
			}
		}
	}
	for (int L = 3; L <= len; L++)
		for (int i = 0; i + L - 1 < len; i++)
		{
			int j = i + L - 1;
			if (S[i] == S[j] && dp[i + 1][j - 1] == 1)
			{
				dp[i][j] = 1;
				ans = L;
			}
		}
	printf("%d",ans);
	return 0;
}