HDU 4991 ordered subsequence (DP + tree array)

Link: HDU 4991 ordered subsequence

Given a sequence, the number of sub-sequences must be m and increase progressively.

Solution: DP [I] [J] indicates that the incremental substring number ending with the number of I and the length of J is selected. You can use a tree array to maintain each number after discretization.

#include <cstdio>#include <cstring>#include <vector>#include <algorithm>#define lowbit(x) ((x)&(-x))using namespace std;typedef long long ll;const int maxn = 10005;const int maxm = 105;const ll mod = 123456789;struct state {    ll val;    int pos, rank;    state (ll val = 0, int pos = 0, int rank = 0) {        this->val = val;        this->pos = pos;        this->rank = rank;    }};int N, M, T;ll dp[maxn][maxm], fenw[maxm][maxn];vector<state> vec;inline bool sort_val(const state& a, const state& b) {    return a.val < b.val;}inline bool sort_pos(const state& a, const state& b) {    return a.pos < b.pos;}void add (ll* f, int x, ll v) {    while (x <= T) {        f[x] = (f[x] + v) % mod;        x += lowbit(x);    }}ll sum (ll* f, int x) {    ll ret = 0;    while (x) {        ret = (ret + f[x]) % mod;        x -= lowbit(x);    }    return ret;}void init () {    ll x;    vec.clear();    for (int i = 1; i <= N; i++) {        scanf("%lld", &x);        vec.push_back(state(x, i));    }    sort(vec.begin(), vec.end(), sort_val);    vec[0].rank = 2;    for (int i = 1; i < N; i++) {        vec[i].rank = vec[i-1].rank;        if (vec[i].val != vec[i-1].val)            vec[i].rank++;    }    T = vec[N-1].rank;    sort(vec.begin(), vec.end(), sort_pos);}ll solve () {    memset(dp, 0, sizeof(dp));    memset(fenw, 0, sizeof(fenw));    add(fenw[0], 1, 1);    for (int i = 1; i <= N; i++) {        for (int j = min(i, M); j >= 1; j--) {            ll tmp = sum(fenw[j-1], vec[i-1].rank - 1);            dp[i][j] = (dp[i][j] + tmp) % mod;            add(fenw[j], vec[i-1].rank, tmp);        }    }    ll ret = 0;    for (int i = 1; i <= N; i++)        ret = (ret + dp[i][M]) % mod;    return ret;}int main () {    while (scanf("%d%d", &N, &M) == 2) {        init();        printf("%lld\n", solve());    }    return 0;}

HDU 4991 ordered subsequence (DP + tree array)