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  • bzoj 1040 基向内环树dp

    #include<bits/stdc++.h>
    #define LL long long
    #define fi first
    #define se second
    #define mk make_pair
    #define pii pair<int, int>
    #define y1 skldjfskldjg
    #define y2 skldfjsklejg
    
    using namespace std;
    
    const int N = 1e6 + 7;
    const int M = 1e5 + 7;
    const int inf = 0x3f3f3f3f;
    const LL INF = 0x3f3f3f3f3f3f3f3f;
    const int mod = 1e9 +7;
    
    int n, tot, a[N], fa[N], b[N], head[N];
    bool vis[N];
    LL f[N][2];
    
    struct Edge {
        int to, nx;
    } edge[N << 1];
    
    void add(int u, int v) {
        edge[tot].to = v;
        edge[tot].nx = head[u];
        head[u] = tot++;
    }
    
    int getRoot(int x) {
        return fa[x] == x ? x : fa[x] = getRoot(fa[x]);
    }
    
    void dp(int u, int fa, int ban) {
        f[u][0] = 0, f[u][1] = a[u];
        LL tmp[2] = {0};
    
        for(int i = head[u]; ~i; i = edge[i].nx) {
            int v = edge[i].to;
            if(v == fa || i == ban || (i ^ 1) == ban) continue;
            dp(v, u, ban);
    
            tmp[0] = f[u][0], tmp[1] = f[u][1];
    
            tmp[0] = max(tmp[0], f[u][0] + f[v][1]);
            tmp[0] = max(tmp[0], f[u][0] + f[v][0]);
            tmp[1] = max(tmp[1], f[u][1] + f[v][0]);
    
            f[u][0] = tmp[0], f[u][1] = tmp[1];
        }
    }
    
    int main() {
        memset(head, -1, sizeof(head));
    
        scanf("%d", &n);
        for(int i = 1; i <= n; i++) {
            scanf("%d%d", &a[i], &b[i]);
            add(i, b[i]); add(b[i], i);
            fa[i] = i;
        }
    
        LL ans = 0;
        for(int i = 1; i <= n; i++) {
            int x = getRoot(i);
            int y = getRoot(b[i]);
            if(x != y) {
                fa[x] = y;
            } else {
                LL ret = 0;
                dp(i, 0, i * 2 - 2);
                ret = max(ret, f[i][0]);
                dp(b[i], 0, i * 2 - 2);
                ret = max(ret, f[b[i]][0]);
                ans += ret;
            }
        }
    
        printf("%lld
    ", ans);
        return 0;
    }
    
    
    /*
    */
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  • 原文地址:https://www.cnblogs.com/CJLHY/p/9360770.html
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