hdu 5396 Expression（区间dp）

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题目链接：hdu 5396 Expression

需要乘上组合数。

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int maxn = 100;const int mod = 1e9 + 7;typedef long long ll;int C[maxn + 5][maxn + 5], F[maxn + 5];int N, dp[maxn + 5][maxn + 5];char order[maxn + 5];void init () {for (int i = 0; i <= maxn; i++) {C[i][0] = C[i][i] = 1;for (int j = 1; j < i; j++)C[i][j] = (C[i-1][j] + C[i-1][j-1]) % mod;}F[0] = 1;for (int i = 1; i <= maxn; i++)F[i] = 1LL * i * F[i-1] % mod;}int main () {init ();while (scanf("%d", &N) == 1) {memset(dp, 0, sizeof(dp));for (int i = 0; i < N; i++) scanf("%d", &dp[i][i]);scanf("%*c");gets(order);N--;for (int i = N-1; i >= 0; i--) {for (int j = i + 1; j <= N; j++) {int len = j - i - 1;for (int k = i; k < j; k++) {int l = k - i, r = j - k - 1;ll ret = 0;if (order[k] == '+') {ret = (ret + 1LL * dp[i][k] * F[r]) % mod;ret = (ret + 1LL * dp[k+1][j] * F[l]) % mod;} else if (order[k] == '-') {ret = (ret + 1LL * dp[i][k] * F[r]) % mod;ret = ((ret - 1LL * dp[k+1][j] * F[l]) % mod + mod) % mod;} else if (order[k] == '*')ret = 1LL * dp[i][k] * dp[k+1][j] % mod;dp[i][j] = (dp[i][j] + ret * C[len][l]) % mod;}//printf("%d %d: %d\n", i, j, dp[i][j]);}}printf("%d\n", dp[0][N]);}return 0;}

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