• BZOJ 4316: 小C的独立集


    4316: 小C的独立集
    思路:先将树上的转移做好。然后环上的转移就是强制最上面的的点选或者不选,然后在环上跑一遍转移就可以了。
    代码:

    #pragma GCC optimize(2)
    #pragma GCC optimize(3)
    #pragma GCC optimize(4)
    #include<bits/stdc++.h>
    using namespace std;
    #define y1 y11
    #define fi first
    #define se second
    #define pi acos(-1.0)
    #define LL long long
    //#define mp make_pair
    #define pb push_back
    #define ls rt<<1, l, m
    #define rs rt<<1|1, m+1, r
    #define ULL unsigned LL
    #define pll pair<LL, LL>
    #define pli pair<LL, int>
    #define pii pair<int, int>
    #define piii pair<pii, int>
    #define pdd pair<double, double>
    #define mem(a, b) memset(a, b, sizeof(a))
    #define debug(x) cerr << #x << " = " << x << "
    ";
    #define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    //head
    
    const int N = 6e4 + 10;
    vector<int> g[N];
    int n, m, u, v, dp[N][2], fa[N];
    int low[N], dfn[N], cnt = 0;
    inline void DP(int u, int v) {
        int now0 = 0, now1 = 0;
        for (int i = v; i != u; i = fa[i]) {
            int t0 = now0 + dp[i][0];
            int t1 = now1 + dp[i][1];
            now0 = max(t0, t1);
            now1 = t0;
        }
        dp[u][0] += now0;
        now0 = 0, now1 = -10000000;
        for (int i = v; i != u; i = fa[i]) {
            int t0 = now0 + dp[i][0];
            int t1 = now1 + dp[i][1];
            now0 = max(t0, t1);
            now1 = t0;
        }
        dp[u][1] += now1;
    }
    inline void tarjan(int u, int o) {
        fa[u] = o;
        dp[u][1] = 1;
        dfn[u] = low[u] = ++cnt;
        for (int i = 0; i < g[u].size(); ++i) {
            int v = g[u][i];
            if(v == o) continue;
            if(!dfn[v]) {
                tarjan(v, u);
                low[u] = min(low[u], low[v]);
            }
            else low[u] = min(low[u], dfn[v]);
            if(low[v] > dfn[u]) {
                dp[u][0] += max(dp[v][0], dp[v][1]);
                dp[u][1] += dp[v][0];
            }
        }
        for (int i = 0; i < g[u].size(); ++i) {
            int v = g[u][i];
            if(fa[v] != u && dfn[v] > dfn[u]) {
                DP(u, v);
            }
        }
    }
    int main() {
        scanf("%d %d", &n, &m);
        for (int i = 1; i <= m; ++i) scanf("%d %d", &u, &v), g[u].pb(v), g[v].pb(u);
        tarjan(1, 0);
        printf("%d
    ", max(dp[1][0], dp[1][1]));
        return 0;
    }
    
    
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  • 原文地址:https://www.cnblogs.com/widsom/p/11460135.html
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