Gym 100507G The Debut Album

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题目 http://codeforces.com/gym/100507

题意：

在n个位置填充1 or 2. 要求连续的1的个数不超过a，连续的2的个数不超过b. 求方案数.

跟以前做过的一道dp题差不多，都是套路
dp[i+j][0] 表示第i个位置填1，在i位置后面连续填j个2的方案个数
dp[i+j][1] 表示第i个位置填2，在i位置后面连续填j个1的方案个数

dp[i+j][0] += dp[i][1]
dp[i+j][1] += dp[i][0]

#include <iostream>#include <algorithm>#include <cstdio>#include <cstring>#include <queue>#include <vector>#include <cmath>#include <stack>#include <string>#include <sstream>#include <map>#include <set>#define pi acos(-1.0)#define LL long long#define ULL unsigned long long#define inf 0x3f3f3f3f#define INF 1e18#define lson l,mid,rt<<1#define rson mid+1,r,rt<<1|1#define debug(a) printf("---%d---\n", a)#define mem0(a) memset(a, 0, sizeof(a))#define memi(a) memset(a, inf, sizeof(a))#define mem1(a) memset(a, -1, sizeof(a))using namespace std;typedef pair<int, int> P;const double eps = 1e-10;const int maxn = 1e6 + 5;const int mod = 1e9 + 7;LL dp[maxn][2];int main(void){//freopen("C:\\Users\\wave\\Desktop\\NULL.exe\\NULL\\in.txt","r", stdin);    int n, a, b;    while (cin >> n >> a >> b)    {        memset(dp, 0, sizeof(dp));        dp[0][0] = dp[0][1] = 1;        for (int i = 0; i <= n; i++){            for (int j = 1; j <= a && i+j <= n; j++)                dp[i + j][0] = (dp[i + j][0] + dp[i][1]) % mod;            for (int j = 1; j <= b && i+j <= n; j++)                dp[i + j][1] = (dp[i + j][1] + dp[i][0]) % mod;        }        cout << (dp[n][0] + dp[n][1]) % mod << endl;    }return 0;}

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