UVALive 4614 Moving to Nuremberg

http://livearchive.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=2615

DFS twice

the first DFS

the dp[u] as the time that edge[father][u] had been used

sum[u] as summary cost  given by  the cost of all nodes in subtree u to u

so

for each son of u

dp[u] <- dp[v] + dp[u]

sum[u] <- sum[v] + dp[v] * w[u][v]

the second time DFS

sum[u] as summary cost given by  the cost of all nodes in whole tree to u

so

sum[u]  <- sum[u] + sum[fa] - sum[u] + (sdp - dp[u] - dp[u]) * w[fa][u]          sdp as the total times to visit all node

#include <iostream>#include <cstring>#include <cstdlib>#include <cstdio>#include <cmath>#include <vector>#include <algorithm>#include <map>using namespace std;#define MAXN 55000#define Rep(c, a, b) for (int c = a; c < b; c++)#define INFI 1e16typedef long long LL;typedef pair<LL, LL> PA;struct  Edge{    int v, w, next;};vector<Edge> E;int L[MAXN];void G_ini(){    E.clear();    memset(L, -1, sizeof L);}void AE(int u, int v, int w){    Edge te = {v, w, L[u]};    L[u] = E.size();    E.push_back(te);}int n, m;LL mn, sdp, dp[MAXN], sum[MAXN];bool vis[MAXN];PA DFS_U(int u){    LL tp = 0, ts = 0;    vis[u] = 1;    for (int i = L[u]; i != -1; i = E[i].next)    {        int v = E[i].v, w = E[i].w;        if (!vis[v])        {            PA td = DFS_U(v);            tp += td.first;            ts += td.first * w + td.second;        }    }    dp[u] += tp;    sum[u] = ts;    return make_pair(dp[u], sum[u]);}void DFS_D(int u, int e){    vis[u] = 1;    if (e != -1)    {        int fa = E[e ^ 1].v, w = E[e].w;        sum[u] += sum[fa] - sum[u] - dp[u] * w;        sum[u] += E[e ^ 1].w * (sdp - dp[u]);    }    mn = min(mn, sum[u]);    for (int i = L[u]; i != -1; i = E[i].next)    {        int v = E[i].v;        if (!vis[v]) DFS_D(v, i);    }}int main(){    int Cas;    scanf("%d", &Cas);    while (Cas--)    {        G_ini();        scanf("%d", &n);        Rep(i, 0, n - 1)        {            int u, v, w;            scanf("%d%d%d", &u, &v, &w);            AE(u, v, w);            AE(v, u, w);        }        scanf("%d", &m);        memset(sum, 0, sizeof sum);        memset(dp, 0, sizeof dp);        sdp = 0;        while (m--)        {            int u, w;            scanf("%d%d", &u, &w);            sdp += w;            dp[u] = w;        }        memset(vis, 0, sizeof vis);        DFS_U(1);        memset(vis, 0, sizeof vis);        mn = INFI;        DFS_D(1, -1);        printf("%lld\n", mn * 2);        int i;        for (i = 1; i <= n; i++) if (sum[i] == mn)        {            printf("%d", i);            break;        }        for (i++; i <= n; i++) if (sum[i] == mn)            printf(" %d", i);        puts("");    }    return 0;}

beside DFS once is enough :)