Expression

3
3 2 1
-+
5
1 4 6 8 3
+*-*

2
999999689
Hint
 Two numbers are considered different when they are in different positions.
 

#include <cstdio>
#include <iostream>
#include <cstring>

using namespace std;
#define LL long long
const int mod = 1000000000 + 7;
const int N = 105;

LL d[N][N];
char s[N];
int n;
LL C[N][N];
LL A[N];

void doit()
{
    A[0] = 1;
    for(int i = 1; i <= 100; i++)
    A[i] = (A[i - 1] * i) % mod;

    memset(C, 0, sizeof C);
    for(int i = 0; i <= 100; i++)
    {
        C[i][0] = 1;
        for(int j = 1; j <= i; j++)
        C[i][j] = (C[i - 1][j - 1] + C[i - 1][j]) % mod;
    }
}

int main()
{
    doit();
    while(~scanf("%d", &n))
    {
        for(int i = 1; i <= n; i++) scanf("%I64d", &d[i][i]);
        scanf("%s", s + 1);

        for(int L = 1; L <= n; L++)
        for(int i = 1; i + L <= n; i++)
        {
            int j = i + L;
            d[i][j] = 0;
            for(int k = i; k < j; k++)
            {
                LL tmp;
                if(s[k] == '*') tmp = (d[i][k] * d[k + 1][j]) % mod;
                else if(s[k] == '+') tmp = (d[i][k] * A[j - k - 1] + d[k + 1][j] * A[k - i]) % mod;
                else tmp = (d[i][k] * A[j - k - 1] - d[k + 1][j] * A[k - i]) % mod;
                d[i][j] = (d[i][j] + tmp * C[j - i - 1][k - i]) % mod;
            }
        }
        printf("%I64d\n", (d[1][n] + mod) % mod);
    }
    return 0;
}

hdu 5396 区间DP

原文：http://blog.csdn.net/dojintian/article/details/47841849