UVALive 3516 Exploring Pyramids (区间dp)

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
using namespace std;
#define ll long long
const int maxn = 310;
const ll mod = 1e9;
char s[maxn];
ll dp[maxn][maxn];

ll solve(int i, int j) {
    if(i == j) return 1;
    if(s[i] != s[j]) return 0;
    ll& ans = dp[i][j];
    if(ans >= 0) return ans;
    ans = 0;
    for(int k = i + 2; k <= j; k++) if(s[i] == s[k]) {
        ans = (ans + solve(i+1, k-1) * solve(k, j)) % mod;
    }
    return ans;
}
int main() {
    while(~scanf("%s", s)) {
        memset(dp, -1, sizeof(dp));
        cout << solve(0, strlen(s) - 1) << endl;
    }
}