• dp


    C. Multiplicity
    time limit per test
    3 seconds
    memory limit per test
    256 megabytes
    input
    standard input
    output
    standard output

    You are given an integer array a1,a2,,an

    .

    The array b

    is called to be a subsequence of a if it is possible to remove some elements from a to get b

    .

    Array b1,b2,,bk

    is called to be good if it is not empty and for every i (1ik) bi is divisible by i

    .

    Find the number of good subsequences in a

    modulo 109+7

    .

    Two subsequences are considered different if index sets of numbers included in them are different. That is, the values ​of the elements ​do not matter in the comparison of subsequences. In particular, the array a

    has exactly 2n1

    different subsequences (excluding an empty subsequence).

    Input

    The first line contains an integer n

    (1n100000) — the length of the array a

    .

    The next line contains integers a1,a2,,an

    (1ai106

    ).

    Output

    Print exactly one integer — the number of good subsequences taken modulo 109+7

    .

    Examples
    Input
    Copy
    2
    1 2
    Output
    Copy
    3
    Input
    Copy
    5
    2 2 1 22 14
    Output
    Copy
    13
    Note

    In the first example, all three non-empty possible subsequences are good: {1}

    , {1,2}, {2}

    In the second example, the possible good subsequences are: {2}

    , {2,2}, {2,22}, {2,14}, {2}, {2,22}, {2,14}, {1}, {1,22}, {1,14}, {22}, {22,14}, {14}

    .

    Note, that some subsequences are listed more than once, since they occur in the original array multiple times.

    题意 : 给你 n 个数字,对于任意位置的数你都可以选择或者不选择,构成一个新的序列,当构成新的序列满足第一个数是1的倍数,第二个数是2的倍数..以此类推询问你方案数有多少

    思路分析 :

      比赛的时候写了一个 dp,顺势推过去的,用 01 数组去优化的一个,dp[i][j] 表示到达第 i 个位置,且当前构成的序列可以整除 j 的方案数,但由于 n 很大,想的是用 01 滚动数组优化个,

    结果凉掉了,就是有些状态是不会被转移过去,从而造成了丢失

      其实一维 dp 就够, dp[i] 表示当前数作为整除 i 的数的个数,倒着推就可以了

    代码示例 :

    #define ll long long
    const ll maxn = 1e6+5;
    const ll maxm = 1e5+5;
    const ll mod = 1e9+7;
    const double eps = 1e-9;
    const double pi = acos(-1.0);
    const ll inf = 0x3f3f3f3f;
    
    ll n;
    ll a[maxm];
    vector<ll>ve[maxn];
    
    void init(){
        for(ll i = 1; i <= 1e6; i++){
            for(ll j = i; j <= 1e6; j += i){
                ve[j].push_back(i);
            }
        } 
    }
    ll dp[maxn];
    void solve(){
        //ll pt = 1;
        //dp[0][0] = 1, dp[1][0] = 1;
        dp[0] = 1; 
        ll ans = 0;
        for(ll i = 1; i <= n; i++){
            for(ll j = ve[a[i]].size()-1; j >= 0; j--){
                ll x = ve[a[i]][j];  
                dp[x] = dp[x]+dp[x-1];
                dp[x] %= mod;
            } 
        }
        for(ll i = 1; i <= n; i++) {
            ans += dp[i];
            ans %= mod;
          //   printf("++++ i = %lld   %lld
    ", i, dp[pt][i]);
        }
        cout << ans << endl;
    }
    
    int main() {
        //freopen("in.txt", "r", stdin);
        //freopen("out.txt", "w", stdout); 
        //init();
        cin >> n ;
        for(ll i = 1; i <= n; i++) scanf("%lld", &a[i]);
        init();
        solve();
        return 0;
    }
    
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  • 原文地址:https://www.cnblogs.com/ccut-ry/p/10010657.html
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