洛谷 #3387. 【模板】縮點

題意

縮點模板，求最大權值和

題解

Tarjan縮點 + Dp

調試記錄

$縮點後head數組沒memset$(鍋已補)

$害得我調了一上午$

#include <cstdio>
#include <stack>
#include <cstring>
#include <queue>
#define maxn 1000005

using namespace std;

struct node{
    int to, next;
}e[maxn];

int n, m, head[maxn], tot = 0, Index = 0, cnt = 0;
bool vis[maxn];
int dfn[maxn], low[maxn], val[maxn];

stack <int> s;

void addedge(int u, int v){ e[++tot] = (node){ v, head[u]}; head[u] = tot; }

int color[maxn], sum[maxn];

void Tarjan(int cur){
    s.push(cur);
    vis[cur] = true;
    dfn[cur] = low[cur] = ++Index;
    
    for (int i = head[cur]; i; i = e[i].next){
        if (!dfn[e[i].to]){
            Tarjan(e[i].to);
            low[cur] = min(low[cur], low[e[i].to]);
        }
        else{
            if (vis[e[i].to]) low[cur] = min(low[cur], dfn[e[i].to]);
        }
    }
    
    if (dfn[cur] == low[cur]){
        cnt++;
        int tmp = 0;
        while (tmp != cur){
            tmp = s.top();
            s.pop();
            color[tmp] = cnt;
            sum[cnt] += val[tmp];
            vis[tmp] = false;
        }
    }
}

int dis[maxn], ans = 0;

void dp(int cur){
    dis[cur] = sum[cur];
    int Max = 0;
    for (int i = head[cur]; i; i = e[i].next){
        if (!dis[e[i].to]) dp(e[i].to);
        Max = max(Max, dis[e[i].to]);
    }
    dis[cur] += Max;
}

int x[maxn], y[maxn];

int main(){
    scanf("%d%d", &n, &m);
    
    for (int i = 1; i <= n; i++) scanf("%d", &val[i]);
    
    for (int i = 1; i <= m; i++){
        scanf("%d%d", &x[i], &y[i]); addedge(x[i], y[i]);
    }
    
    for (int i = 1; i <= n; i++)
        if (!dfn[i]) Tarjan(i);
    
    tot = 0;
    memset(e, 0, sizeof e);
    memset(vis, false, sizeof vis);
    memset(head, 0, sizeof head);
    
    for (int i = 1; i <= m; i++){
        if (color[x[i]] != color[y[i]]){
            addedge(color[x[i]], color[y[i]]);
        }
    }
    
    for (int i = 1; i <= cnt; i++) 
        if (!dis[i]) dp(i), ans = max(ans, dis[i]);
    printf("%d\n", ans);
    
    return 0;
}