HDU 4745 Two Rabbits (最长回文变形)

/*31ms,4192KB*/

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int mx = 1005;

int dp[mx][mx];///从i到j的最长回文串的长度
int w[mx];

int solve(int n)
{
	int i, j;
	memset(dp, 0, sizeof(dp));
	for (i = 1; i <= n; ++i) dp[i][i] = 1;
	for (i = n - 1; i; --i)
		for (j = i + 1; j <= n; ++j)
			if (w[i] == w[j]) dp[i][j] = max(dp[i][j], dp[i + 1][j - 1] + 2);
			else dp[i][j] = max(dp[i + 1][j], dp[i][j - 1]);
			
	///枚举起点。针对每个起点，两边的最长回文串的长度之和就是从这里出发的最大值
	///注意把[1,n]区间也算上
	int ans = 0;
	for (i = 1; i <= n; ++i) ans = max(ans, dp[1][i] + dp[i + 1][n]);
	return ans;
}

int main()
{
	int n, i;
	while (scanf("%d", &n), n)
	{
		for (i = 1; i <= n; ++i) scanf("%d", &w[i]);
		printf("%d\n", solve(n));
	}
	return 0;
}