codevs 2370 小机房的树 (lca)

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学习了Tarjan求lca，结果是dep[u]+dep[v]-2*dep[lca]

#include <stdio.h>#include <string.h>const int MAXN = 5e4+10;const int MAXQ = 8e4+10;int F[MAXN];int getf(int x){    if(F[x] == -1) return x;    return F[x] = getf(F[x]);}void bing(int u, int v){    int t1 = getf(u);    int t2 = getf(v);    if(t1 != t2)        F[t1] = t2;}bool vis[MAXN];int ancestor[MAXN];struct Edge{    int to,next,w;}edge[MAXN*2];int head[MAXN],tot;int dep[MAXN];void addedge(int u, int v, int w){    edge[tot].to = v;    edge[tot].w = w;    edge[tot].next = head[u];    head[u] = tot++;}struct Query{    int q,next;    int index;}query[MAXQ*2];int answer[MAXQ];int h[MAXQ];int tt;int Q;void add_query(int u, int v, int index){    query[tt].q = v;    query[tt].next = h[u];    query[tt].index = index;    h[u] = tt++;}void init(){    tot = tt = 0;    memset(head,-1,sizeof(head));    memset(dep,0,sizeof(dep));    memset(h,-1,sizeof(h));    memset(vis,0,sizeof(vis));    memset(F,-1,sizeof(F));    memset(ancestor,0,sizeof(ancestor));}void LCA(int u, int depth){    dep[u] = depth;    ancestor[u] = u;    vis[u] = true;    for(int i = head[u]; i != -1; i = edge[i].next)    {        int v = edge[i].to;        if(vis[v]) continue;        LCA(v,depth+edge[i].w);        bing(u,v);        ancestor[getf(u)] = u;    }    for(int i = h[u]; i != -1; i = query[i].next)    {        int v = query[i].q;        if(vis[v])        {            answer[query[i].index] = dep[u] + dep[v] - 2*dep[ancestor[getf(v)]];        }    }}int main(){    int n,u,v,w;    while(scanf("%d",&n) != EOF)    {        init();        for(int i = 1; i <= n-1; ++i)        {            scanf("%d %d %d",&u,&v,&w);            u++;            v++;            addedge(u,v,w);            addedge(v,u,w);        }        scanf("%d",&Q);        for(int i = 1; i <= Q; ++i)        {            scanf("%d %d",&u,&v);            u++;            v++;            add_query(u,v,i);            add_query(v,u,i);        }        LCA(1,0);        for(int i = 1; i <= Q; ++i)            printf("%d\n",answer[i]);    }    return 0;}

学习了倍增lca，wa了好久发现写错变量了

#include <bits/stdc++.h>using namespace std;typedef long long LL;const int MAXN = 1e5+10;const int DEG = 20;struct Edge{    int to,next,w;}edge[MAXN*2];int head[MAXN],tot;void addedge(int u, int v, int w){    edge[tot].to = v;    edge[tot].w = w;    edge[tot].next = head[u];    head[u] = tot++;}void init(){    tot = 0;    memset(head,-1,sizeof(head));}int fa[MAXN][DEG];LL cost[MAXN][DEG];int deg[MAXN];void BFS(int root){    queue<int> que;    deg[root] = 0;    fa[root][0] = root;    cost[root][0] = 0;    que.push(root);    while(!que.empty())    {        int tmp = que.front();        que.pop();        for(int i = 1; i < DEG; ++i)        {            fa[tmp][i] = fa[fa[tmp][i-1]][i-1];            cost[tmp][i] = cost[tmp][i-1] + cost[fa[tmp][i-1]][i-1];        }        for(int i = head[tmp]; i != -1; i = edge[i].next)        {            int v = edge[i].to;            if(v == fa[tmp][0]) continue;            deg[v] = deg[tmp]+1;            fa[v][0] = tmp;            cost[v][0] = edge[i].w;            que.push(v);        }    }}LL LCA(int u, int v){    LL ret = 0;    if(deg[u] > deg[v]) swap(u,v);    int hu = deg[u], hv = deg[v];    int tu = u, tv = v;    for(int det = hv-hu, i = 0; det; det >>=1, ++i)    {        if(det&1)        {            ret += cost[tv][i];            tv = fa[tv][i];        }    }    if(tv == tu) return ret;    for(int i = DEG-1; i >= 0; --i)    {        if(fa[tu][i] == fa[tv][i])            continue;        ret += cost[tu][i];        ret += cost[tv][i];        tu = fa[tu][i];        tv = fa[tv][i];    }    if(tu != tv)        ret += (cost[tu][0]+cost[tv][0]);    return ret;}int main(){    init();    int n,u,v,w;    scanf("%d",&n);    for(int i = 0; i < n-1; ++i)    {        scanf("%d %d %d",&u,&v,&w);        addedge(u,v,w);        addedge(v,u,w);    }    int q;    BFS(1);    scanf("%d",&q);    while(q--)    {        scanf("%d %d",&u,&v);        printf("%lld\n",LCA(u,v));    }    return 0;}

ST在线

#include <bits/stdc++.h>using namespace std;typedef long long LL;const int MAXN = 100010;int rmq[2*MAXN];struct ST{    int mm[2*MAXN];    int dp[2*MAXN][20];    void init(int n)    {        mm[0] = -1;        for(int i = 1; i <= n; i++)        {            mm[i] = ((i&(i-1)) == 0)?mm[i-1]+1:mm[i-1];            dp[i][0] = i;        }        for(int j = 1; j <= mm[n]; j++)            for(int i = 1; i + (1<<j) - 1 <= n; i++)                dp[i][j] = rmq[dp[i][j-1]] <                           rmq[dp[i+(1<<(j-1))][j-1]]?dp[i][j-1]:dp[i+(1<<(j-1))][j-1];    }    int query(int a,int b)    {        if(a > b)swap(a,b);        int k = mm[b-a+1];        return rmq[dp[a][k]] <=               rmq[dp[b-(1<<k)+1][k]]?dp[a][k]:dp[b-(1<<k)+1][k];    }};struct Edge{    int to,next,w;};Edge edge[MAXN*2];int tot,head[MAXN];LL dist[MAXN];int F[MAXN*2];int P[MAXN];int cnt;ST st;void init(){    tot = 0;    memset(head,-1,sizeof(head));}void addedge(int u, int v, int w)//加边，无向边需要加两次{    edge[tot].to = v;    edge[tot].w = w;    edge[tot].next = head[u];    head[u] = tot++;}void dfs(int u,int pre,int dep){    F[++cnt] = u;    rmq[cnt] = dep;    P[u] = cnt;    for(int i = head[u]; i != -1; i = edge[i].next)    {        int v = edge[i].to;        if(v == pre)continue;        dist[v] = dist[u] + edge[i].w;        dfs(v,u,dep+1);        F[++cnt] = u;        rmq[cnt] = dep;    }}void LCA_init(int root,int node_num)//查询LCA前的初始化{    cnt = 0;    dfs(root,root,0);    st.init(2*node_num-1);}int query_lca(int u,int v)//查询u,v的lca编号{    return F[st.query(P[u],P[v])];}int main(){    int N;    int u,v,w;    scanf("%d",&N);    init();    for(int i = 1; i < N; i++)    {        scanf("%d%d%d",&u,&v,&w);        addedge(++u,++v,w);        addedge(v,u,w);    }    LCA_init(1,N);    int q;    scanf("%d",&q);    while(q--)    {        scanf("%d%d",&u,&v);        printf("%lld\n",dist[++u]+dist[++v]-2*dist[query_lca(u,v)]);    }    return 0;}

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