UVa 10617 Again Palindrome（回文串区间DP）

   于是 dp[i][j] = dp[i+1][j] + dp[i][j-1] - dp[i+1][j-1];

<span style="font-size:18px;">#include <cstdio>
#include <iostream>
#include <cstring>
#include <cmath>
#include <string>
#include <algorithm>
#include <queue>
#include <stack>
using namespace std;

#define ll long long
const double PI = acos(-1.0);
const double e = 2.718281828459;
const double eps = 1e-8;
const int MAXN = 65;
ll dp[MAXN][MAXN];
char s[MAXN];

int main()
{
    //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    int Case;
    cin>>Case;
    while(Case--)
    {
        scanf("%s", s+1);
        int len = strlen(s+1);
        memset(dp, 0, sizeof(dp));
        for(int i = 1; i <= len; i++)
        {
            dp[i][i] = 1;
        }
        for(int k = 2; k <= len; k++)
        {
            for(int i = 1, j = k; j <= len; i++, j++)
            {
                if(s[i] == s[j])
                    dp[i][j] = dp[i+1][j]+dp[i][j-1]+1;
                else
                    dp[i][j] = dp[i+1][j]+dp[i][j-1]-dp[i+1][j-1];
            }
        }
        cout<<dp[1][len]<<endl;
    }
    return 0;
}</span>

<span style="font-size:18px;">#include <cstdio>
#include <iostream>
#include <cstring>
#include <cmath>
#include <string>
#include <algorithm>
#include <queue>
#include <stack>
using namespace std;

#define ll long long
#define max(a, b) (a)>(b)?(a):(b)
const double PI = acos(-1.0);
const double e = 2.718281828459;
const double eps = 1e-8;
const int MAXN = 65;
ll dp[MAXN][MAXN];
char s[MAXN];

ll dfs(int l, int r)
{
    if(dp[l][r] != -1)
        return dp[l][r];
    if(l >= r)
        return dp[l][r] = (l==r)?1:0;
    if(s[l] == s[r])
        dp[l][r] = max(dp[l][r], dfs(l+1, r)+dfs(l, r-1)+1);
    else
        dp[l][r] = max(dp[l][r], dfs(l+1, r)+dfs(l, r-1)-dfs(l+1, r-1));
    return dp[l][r];
}

int main()
{
    //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    int Case;
    cin>>Case;
    while(Case--)
    {
        scanf("%s", s+1);
        int len = strlen(s+1);
        memset(dp, -1, sizeof(dp));
        dp[1][len] = dfs(1, len);
        cout<<dp[1][len]<<endl;
    }
    return 0;
}</span>

UVa 10617 Again Palindrome（回文串区间DP）

原文：http://blog.csdn.net/u014028317/article/details/45339235