CF894E Ralph and Mushrooms_强连通分量_记忆化搜索_缩点

Code:

#include<cstdio>
#include<stack>
#include<cstring>
using namespace std;
const int maxn = 1000000 + 3;
stack<int>S;
int head[maxn], nex[maxn], val[maxn], to[maxn], cnt, n, m, s;
int low[maxn], dfn[maxn], vis[maxn], answer[maxn],  idx, scc;
long long quan[maxn];
inline void add_edge(int u, int v, int c)
{
    nex[++cnt] = head[u];
    head[u] = cnt;
    to[cnt] = v;
    val[cnt] = c;
}
void tarjan(int u)
{
    vis[u] = 1;
    S.push(u);
    low[u] = dfn[u] = ++scc;
    for(int v = head[u]; v ; v = nex[v])
    {
        if(!vis[to[v]])
        {
            tarjan(to[v]);
            low[u] = min(low[u], low[to[v]]);
        }
        else if(!answer[to[v]]) low[u] = min(low[u], dfn[to[v]]);
    }
    if(low[u] == dfn[u])
    {
        ++idx;
        for(;;)
        {
            int x = S.top(); S.pop();
            answer[x] = idx;
            if(x == u) break;
        }
    }
}
struct Math
{
    long long  sum[100097];
    long long C[100097];
    inline void init()
    {
        sum[0] = -1;
        for(int i = 2;i <= 100007; ++i) sum[i] = sum[i - 1] + i - 1;
        for(int i = 1;i <= 100007; ++i) C[i] = sum[i] + C[i - 1];              //第 (i + 1) 项的总和
    }
    inline long long get(int w)
    {
        int l = 1, r = 100000, ans = 0;
        while(l <= r)
        {
            int mid = (l + r) >> 1;
            if(sum[mid] <= w) ans = mid, l = mid + 1;
            else r = mid - 1;
        }
        return (long long) ans * w - C[ans];
    }
}M;
int head2[maxn], to2[maxn << 1], nex2[maxn << 1], cnt2, val2[maxn];
inline void add_edge2(int u,int v, int c)
{
    nex2[++cnt2] = head2[u];
    head2[u] = cnt2;
    to2[cnt2] = v;
    val2[cnt2] = c;
}
long long final[maxn];
long long dp(int u)
{
    if(final[u] != -1) return final[u];
    final[u] = quan[u];
    for(int v = head2[u]; v ; v = nex2[v])
    {
        final[u] = max(final[u], quan[u] + val2[v] + dp(to2[v]));
    }
    return final[u];
}
int main()
{
    scanf("%d%d",&n,&m);
    M.init();
    for(int i = 1;i <= m; ++i)
    {
        int a, b, c;
        scanf("%d%d%d",&a, &b, &c);
        add_edge(a, b, c);
    }
    scanf("%d",&s);
    for(int i = 1;i <= n; ++i)
    {
        if(!vis[i]) tarjan(i);
    }
    for(int i = 1;i <= n; ++i)
    {
        for(int v = head[i]; v ; v = nex[v])
        {
            if(answer[i] == answer[to[v]])
            {
                quan[answer[i]] += M.get(val[v]);
            }
            else
            {
                add_edge2(answer[i], answer[to[v]], val[v]);
            }
        }
    }
    memset(final, -1, sizeof(final));
    printf("%I64d",dp(answer[s]));
    return 0;
}