hdu1513 Palindrome

思路：

dp+滚动数组。

实现：

#include <iostream>
#include <cstdio>
#include <string>
#include <algorithm>
#include <cstring>
using namespace std;

int n;
string str;
int dp[5005][3];

int solve()
{
    for (int i = n - 1; i >= 0; i--)
    {
        for (int j = i + 1; j < n; j++)
        {
            if (str[i] == str[j])
            {
                dp[i & 1][j] = dp[(i + 1) & 1][j - 1];
            }
            else
            {
                dp[i & 1][j] = min(dp[i & 1][j - 1], dp[(i + 1) & 1][j]) + 1;
            }
        }
    }
    return dp[0][n - 1];
}

int solve2()
{
    for (int j = 2; j <= n; j++)
    {
        for (int i = 0; i <= n - j; i++)
        {
            if (str[i] == str[i + j - 1])
            {
                dp[i][j % 3] = dp[i + 1][(j - 2) % 3];
            }
            else
            {
                dp[i][j % 3] = min(dp[i][(j - 1) % 3], dp[i + 1][(j - 1) % 3]) + 1;
            }
        }
    }
    return dp[0][n % 3];
}
int main()
{
    while (cin >> n >> str)
    {
        memset(dp, 0, sizeof(dp));
        cout << solve2() << endl;
    }
    return 0;
}