树上每个元素有一个p,元素之间有距离d,计算一个元素u，使得sigma(d(i,u)*pi)最小。
两次dfs，第一次计算本节点以下的sigma()，第二次利用sump求解出ans。
1 #include <cstdio> 2 #include <algorithm> 3 #include <cstring> 4 #include <vector> 5 #include <map> 6 7 using namespace std; 8 9 const int maxn = 100000+10; 10 11 int fa[maxn]; 12 long long N,chp[maxn],ans[maxn],chsum[maxn],save_p[maxn],save_up[maxn]; 13 long long sump; 14 long long final_ans; 15 int ans_idx; 16 17 vector <int> G[maxn]; 18 map<pair<int,int> ,int> save_dis; 19 20 void dfs(int u,int p) 21 { 22 int d = G[u].size(); 23 for(int i=0;i<d;i++) 24 { 25 int v = G[u][i]; 26 if(p != v) 27 { 28 chp[u] += save_p[v]; 29 dfs(v,fa[v] = u); 30 chp[u] += chp[v]; 31 chsum[u] += (chsum[v]+ save_dis[pair<int,int>(u,v)] *(save_p[v]+chp[v])); 32 } 33 } 34 //printf("index:%d chsum:%d ",u,chsum[u]); 35 } 36 37 38 void solve(int u,int p) 39 { 40 int d = G[u].size(); 41 int disp = save_dis[pair<int,int>(u,p)]; 42 43 if(p != -1) 44 { 45 ans[u] =chsum[u] + (ans[p]-(chsum[u]+disp*(save_p[u]+chp[u]))) + disp*(sump-chp[u]-save_p[u]); 46 //final_ans = min(ans[u],final_ans); 47 //printf("index:%d ans:%d chp:%d dis:%d ",u,ans[u],chp[u],disp); 48 if(final_ans > ans[u]) 49 { 50 ans_idx = u; 51 final_ans = ans[u]; 52 } 53 } 54 55 for(int i=0;i<d;i++) 56 { 57 int v = G[u][i]; 58 if(p != v) 59 { 60 solve(v,u); 61 } 62 } 63 } 64 65 int main() 66 { 67 freopen("house.in","r",stdin); 68 freopen("house.out","w",stdout); 69 70 scanf("%d",&N); 71 for(int i=1;i<=N;i++) 72 { 73 scanf("%d",&save_p[i]); 74 sump += save_p[i]; 75 } 76 for(int i=0;i<N-1;i++) 77 { 78 int u,v,dis; 79 scanf("%d%d%d",&u,&v,&dis); 80 G[u].push_back(v); 81 G[v].push_back(u); 82 83 save_dis[pair<int,int>(u,v)] = dis; 84 save_dis[pair<int,int>(v,u)] = dis; 85 86 } 87 88 int root = 1; 89 fa[root] = -1; 90 dfs(root,-1); 91 92 ans[root] = chsum[root]; 93 final_ans = ans[root]; 94 ans_idx = root; 95 solve(root,-1); 96 printf("%d %lld ",ans_idx,final_ans); 97 }