UVa1362 Exploring Pyramids

 

区间dp，枚举走完第一个子树之后回到根节点的位置。 

 

/*by SilverN*/
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<vector>
using namespace std;
const int mod=1e9;
const int mxn=310;
int read(){
    int x=0,f=1;char ch=getchar();
    while(ch<'0' || ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0' && ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
char s[mxn];
int f[mxn][mxn];
int main(){
    int i,j;
    while(scanf("%s",s+1)!=EOF){
        int n=strlen(s+1);
        memset(f,0,sizeof f);
        for(i=1;i<=n;i++)f[i][i]=1;
        for(int st=2;st<=n;st++){
            for(i=1;i<=n;i++){
                j=i+st-1;if(j>n)break;
                if(s[i]==s[j]){
                    for(int k=i+2;k<=j;k++){
                        if(s[k]==s[i]){
                            f[i][j]=((long long)f[i][j]+((long long)f[i+1][k-1]*f[k][j])%mod)%mod;
                        }
                    }
                }
            }
        }
        printf("%d\n",f[1][n]);
    }
    return 0;
}