AtCoder Beginner Contest 070 D

D - Transit Tree Path

Description

Input

Output

Sample Input

51 2 11 3 12 4 13 5 13 12 42 34 5

Sample Output

324

Hint

题意

51 2 11 3 12 4 13 5 13 12 42 34 5

题解：

324

AC代码

DFS 代码

#include <bits/stdc++.h>using namespace std;#define LL long long#define CLR(a,b) memset(a,(b),sizeof(a))const int INF = 0x3f3f3f3f;const LL INFLL = 0x3f3f3f3f3f3f3f3f;const int N = 1e5+10;vector<pair<int,int> > G[N];LL par[N];int dfs(int x,int y){    for(int i = 0; i < G[x].size(); i++) {        int j = G[x][i].first;        if(j == y) continue;        par[j] = par[x] + G[x][i].second;        dfs(j, x);    }}int main(){    int n;    int x, y, z;    scanf("%d",&n);    for(int i = 0; i < n-1; i++) {        scanf("%d%d%d",&x,&y,&z);        G[x].push_back(make_pair(y,z));        G[y].push_back(make_pair(x,z));    }    int q, k;    scanf("%d%d",&q,&k);    par[k] = 0; dfs(k, -1);    while(q--) {        scanf("%d%d",&x,&y);        printf("%lld\n",par[x]+par[y]);    }return 0;}

LCA代码

#include<bits/stdc++.h>using namespace std ;typedef long long LL ;const int MAXN = 1e5+100 ;const int MAXM = 1e5 ;const int mod  = 1e9+7 ;struct Edge {    LL from,to,val,next;}edge[MAXN<<2];LL head[MAXN],top;LL n,m;void init(){    memset(head,-1,sizeof(head));    top=0;}void addedge(LL a,LL b,LL c){    Edge e={a,b,c,head[a]};    edge[top]=e;head[a]=top++;}void getmap(){     LL a,b,c;     while(m--){        scanf("%lld%lld%lld",&a,&b,&c);        addedge(a,b,c);        addedge(b,a,c);     }}LL fa[MAXN][50+5],depth[MAXN];LL dist[MAXN];void dfs(LL now,LL par){    fa[now][0]=par;    for(LL i=1;i<50;i++){        fa[now][i]=fa[fa[now][i-1]][i-1];    }    for(LL i=head[now];i!=-1;i=edge[i].next){        Edge e=edge[i];        if(e.to!=par){            dist[e.to]=dist[now]+e.val;            depth[e.to]=depth[now]+1;            dfs(e.to,now);        }    }}LL lca(LL a,LL b){    if(depth[a]<depth[b]) swap(a,b);    for(LL i=49;i>=0;i--){        if(depth[fa[a][i]]>=depth[b]){            a=fa[a][i];        }    }    if(a==b) return b;    for(LL i=49;i>=0;i--){        if(fa[a][i]!=fa[b][i]){            a=fa[a][i];            b=fa[b][i];        }    }    return fa[b][0];}void solve(){    depth[1]=0;dist[1]=0;    dfs(1,-1);    LL q,k;    scanf("%lld%lld",&q,&k);    while(q--){        LL a,b;        scanf("%lld%lld",&a,&b);        LL dis1=dist[a]+dist[k]-2*dist[lca(a,k)];        LL dis2=dist[b]+dist[k]-2*dist[lca(b,k)];        printf("%lld\n",dis1+dis2);    }}int main(){        scanf("%lld",&n);m=n-1;        init();        getmap();        solve();}