[BZOJ 5158][Tjoi2014]Alice and Bob

传送门

\(\color{green}{solution}\)

贪心

/**************************************************************
    Problem: 5158
    User: MiEcoku
    Language: C++
    Result: Accepted
    Time:420 ms
    Memory:5980 kb
****************************************************************/

#include <bits/stdc++.h>
using namespace std;

const int maxn = 100010;

struct Edge {
    int v; Edge *next;
    Edge (int v, Edge *next) : v(v), next(next) {}
    Edge () {}
}*head[maxn], pool[maxn << 1], *pis = pool;

int val[maxn], rd[maxn], top[maxn], n, cnt;
long long ans;
inline void link(int a, int b) {
    head[a] = new (pis ++)Edge(b, head[a]); rd[b]++;
}
priority_queue<int> q;
int tr[maxn << 2];
inline void modify(int c, int l, int r, int L, int o) {
    if( l == r) { tr[c] = o; return;}
    int mid = l + r >> 1;
    if( L <= mid) modify(c << 1, l, mid, L, o);
    else modify(c << 1|1, mid+1, r, L, o);
    tr[c] = max(tr[c << 1], tr[c << 1|1]);
}
int qry(int c, int l, int r, int L) {
    if( r <= L) return tr[c];
    int mid = l + r >> 1;
    if( L <= mid) return qry(c << 1, l, mid, L);
    return max(tr[c << 1], qry(c << 1|1, mid+1, r, L));
}
int main() {
    scanf("%d", &n);
    for ( register int i = 1, x; i <= n; ++ i) {
        scanf("%d", &x); if( (x-1)) link(top[x-1], i);
        if( top[x]) link(i, top[x]); top[x] = i;
    }
    for ( register int i = 1; i <= n; ++ i)
        if( !rd[i]) q.push(i);
    while ( !q.empty()) {
        int u = q.top(); q.pop();
        val[u] = ++cnt;
        for ( Edge *now = head[u]; now; now = now->next)
            if( !(--rd[now->v])) q.push(now->v);
    }
    for ( register int i = n, ret; i; -- i) {
        ret = 1 + qry(1, 1, n, val[i]);
        modify(1, 1, n, val[i], ret); ans += ret;
    }
    printf("%lld\n", ans);
}

---