bzoj1996: [Hnoi2010]chorus 合唱队

题目链接

题解

代码

#include<cstdio>
#include<algorithm>
#define mod 19650827
const int maxn = 1007;
inline int read() {
int x = 0,f = 1;
char c = getchar();
while(c < '0' || c > '9') {if(c == '-')f = -1;c = getchar();}
while(c <= '9' && c >= '0') x = x * 10 + c - '0',c = getchar();
return x * f;
}
int n;
int dp[maxn][maxn][2],a[maxn];
int main() {
n = read();
for(int i = 1;i <= n;++ i) a[i] = read();
for(int i = 1;i <= n;++ i) dp[i][i][0]  = 1;
for(int i = n;i >= 1;-- i)
for(int j = i + 1;j <= n;++ j) {
if(a[j] > a[i]) dp[i][j][1] += dp[i][j - 1][0];
if(a[j] > a[j - 1]) dp[i][j][1] += dp[i][j - 1][1];
if(a[i] < a[j]) dp[i][j][0] += dp[i + 1][j][1];
if(a[i] < a[i + 1]) dp[i][j][0] += dp[i + 1][j][0];
dp[i][j][1] %= mod;
dp[i][j][0] %= mod;
}
printf("%d\n",(dp[1]
[0] + dp[1]
[1]) % mod);
return 0;
}