BZOJ 3870: Our happy ending( 状压dp )

dp(i, s)表示考虑了前i个数后, 能取到的数的集合为s时的方案数.对于1~min(L, K)枚举更新, 剩下的直接乘就好了. 复杂度O(T*K*2^N)。。。好像有点大, 但是可以AC。。。。

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#include<cstdio>

#include<cstring>

#include<algorithm>

using namespace std;

typedef long long ll;

#define b(i) (1 << (i))

const int MOD = 1000000007;

int N, g, L, dp[b(21)];

inline void upd(int &x, int t) {

if((x += t) >= MOD) x -= MOD;

}

int main() {

int T;

scanf("%d", &T);

while(T--) {

scanf("%d%d%d", &N, &g, &L);

memset(dp, 0, sizeof dp);

dp[1] = 1;

int All = b(g + 1) - 1;

while(N--) {

for(int s = All; s; s--) if(dp[s]) {

int t = dp[s];

for(int i = min(g, L); i; i--)

upd(dp[s | ((s << i) & All) | b(i)], t);

if(L > g) upd(dp[s], ll(t) * (L - g) % MOD);

}

int ans = 0;

for(int i = All; i; i--)

if(i & b(g)) upd(ans, dp[i]);

printf("%d\n", ans);

}

return 0;

}

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3870: Our happy ending

Time Limit: 10 Sec Memory Limit: 256 MB
Submit: 146 Solved: 84
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Description

There is an old country and the king fell in love with a devil. The devil always asks the king to do some crazy things. Although the king used to be wise and beloved by his people. Now he is just like a boy in love and can’t refuse any request from the devil. Also, this devil is looking like a very cute Loli.

Y*wan still remember the day he first meets the devil. Now everything is done and the devil is gone. Y*wan feel very sad and suicide.

You feel guilty after killing so many loli, so you suicide too.

Nobody survive in this silly story, but there is still some hope, because this is just a silly background story during one programming contest!

And the last problem is:

Given a sequence a_1,a_2,...,a_n, if we can take some of them(each a_i can only be used once), and they sum to k, then we say this sequence is a good sequence.

How many good sequence are there? Given that each a_i is an integer and 0<= a_i <= L.

You should output the result modulo 10^9+7.

Input

The first line contains an integer T, denoting the number of the test cases.

For each test case, the first line contains 3 integers n, k, L.

T<=20, n,k<=20 , 0<=L<=10^9.

Output

For each cases, output the answer in a single line.

Sample Input

1
2 2 2

Sample Output

HINT

Source

By WJMZBMR

转载于:https://www.cnblogs.com/JSZX11556/p/5175910.html