poj 1986——Distance Queries

来源：互联网发布：因特网属于什么网络编辑：程序博客网时间：2024/06/01 08:18

题意：求树上两点间距离

思路:LCA。用来测试LCA的模板~

用DP维护：

#include<cstdio>#include<cstdlib>#include<iostream>#include<cstring>#include<map>#include<set>#include<list>#include<stack>#include<algorithm>#include<queue>#include<vector>#include<time.h>#include<iomanip>#include<assert.h>using namespace std;const int maxn = 100005;struct Edge{    int u,v,w;    int id;    int next;}edge[maxn*2];int tot ;int first[maxn];void add(int uu,int vv,int ww,int id){    edge[tot].u = uu;    edge[tot].v = vv;    edge[tot].w = ww;    edge[tot].id = id;    edge[tot].next = first[uu];    first[uu] = tot++;}int n,m;int dep[maxn];int pre[maxn];int dp[17][maxn];int q[maxn],qh,qt;int recE[maxn];int recN[maxn];int dis[maxn];void bfs(int u) {    qh = qt = 0;    q[qt ++] = u;    for (int j = 0; j < 17; ++ j) dp[j][0] = -1;    dep[u] = 0;    dis[0] = 0;    pre[u] = -1;    while (qh != qt) {        u = q[qh ++];        for (int now = first[u], v; now != -1; now = edge[now].next)            if (dp[0][u] != (v = edge[now].v)) {                dp[0][v] = u;                for (int j = 1; j < 17; ++ j) {                    if (dp[j - 1][v] == -1) {                        dp[j][v] = -1;                    } else {                        dp[j][v] = dp[j - 1][dp[j - 1][v]];                    }                }                q[qt ++] = v;                dep[v] = dep[u] + 1;                pre[v] = edge[now].id;                dis[v] = dis[u] + edge[now].w;            }    }}int lca(int u, int v) {    if (dep[u] < dep[v]) swap(u, v);    int del = dep[u] - dep[v];    for (int j = 16; j >= 0; -- j)        if (del >> j & 1) u = dp[j][u];    for (int j = 16; j >= 0; -- j)        if (dp[j][u] != dp[j][v]) {            u = dp[j][u];            v = dp[j][v];        }    if (u != v) u = dp[0][u];    return u;}inline bool scan_d(int &ret){    char c;int sgn;    if(c = getchar(),c == EOF)return 0;    while(c!='-' && (c<'0'||c>'9'))c = getchar();    sgn = (c == '-')?-1:1;    ret = (c == '-')?0 :c-'0';    while(c = getchar(),c>='0'&&c<='9')ret = ret*10 + (c-'0');    ret *=sgn;    return 1;}int col[maxn];void putint(int x){    if(x<0){putchar('-'); x *= -1;}    if(x == 0){        putchar('0');        return;    }    char s[20];    int cur = 0;    while(x!=0){        s[cur++] = '0' + x%10;        x/=10;    }    for(int i = cur-1;i>=0;i--){        putchar(s[i]);    }}int main(){//    freopen("data.txt","r",stdin);    tot = 0;memset(first,-1,sizeof(first));    scan_d(n);scan_d(m);    for(int i = 0; i < n-1;++i){        int u,v,w;        scan_d(u);scan_d(v);scan_d(w);        u--;v--;        add(u,v,w,i);        add(v,u,w,i);    }    dep[0] = 0;    pre[0] = -1;    bfs(0);    scan_d(m);    for(int i = 0; i < m; ++i){        int u,v;        scan_d(u);scan_d(v);        u--;v--;        int p = lca(u,v);        putint(dis[u] - dis[p] + dis[v] - dis[p]);        puts("");    }    return 0;}

tarjan离线：

#include<cstdio>#include<cstdlib>#include<iostream>#include<cstring>#include<map>#include<set>#include<list>#include<stack>#include<algorithm>#include<queue>#include<vector>#include<time.h>#include<iomanip>#include<assert.h>using namespace std;const int maxn = 100005;typedef long long ll;struct Edge{    int v;    int next;    int w;    int id;}edge[maxn*4];int tot ;int first[maxn];int firstQuery[maxn];int father[maxn];int fa[maxn];int node[maxn][2];int dis[maxn];int lca[maxn];int find(int x){    return fa[x] = fa[x] == x? x:find(fa[x]);}void add(int uu,int vv,int ww){    edge[tot].v = vv;    edge[tot].w = ww;    edge[tot].next = first[uu];    first[uu] = tot++;}void addQuery(int u,int v){    edge[tot].v = v;    edge[tot].next = firstQuery[u];    firstQuery[u] = tot++;}int n,m;inline bool scan_d(int &ret){    char c;int sgn;    if(c = getchar(),c == EOF)return 0;    while(c!='-' && (c<'0'||c>'9'))c = getchar();    sgn = (c == '-')?-1:1;    ret = (c == '-')?0 :c-'0';    while(c = getchar(),c>='0'&&c<='9')ret = ret*10 + (c-'0');    ret *=sgn;    return 1;}void putint(int x){    if(x<0){putchar('-'); x *= -1;}    if(x == 0){        putchar('0');        return;    }    char s[20];    int cur = 0;    while(x!=0){        s[cur++] = '0' + x%10;        x/=10;    }    for(int i = cur-1;i>=0;i--){        putchar(s[i]);    }}bool vis[maxn];void dfs(int u){    vis[u] = true;    for(int e = first[u]; ~e; e = edge[e].next) {        int v = edge[e].v;        if (v == father[u]) continue;        dis[v] = dis[u] + edge[e].w;        father[v] = u;        dfs(v);        fa[find(v)] = find(u);    }    for(int e = firstQuery[u];~e ; e = edge[e].next) {        int v = edge[e].v;        int cnt = vis[node[v][0]] + vis[node[v][1]];        if (cnt == 2) {            if (node[v][0] == u) {                lca[v] = find(node[v][1]);            } else {                lca[v] = find(node[v][0]);            }        }    }}void solve() {    scan_d(n);scan_d(m);    for(int i = 0; i < n; ++ i) {        vis[i] = false;        first[i] = -1;        firstQuery[i] = -1;        fa[i] = i;    }    tot = 0;    int u, v,w;    for(int i = 0; i < n - 1; ++ i) {        scan_d(u);        scan_d(v);        scan_d(w);        --u, --v;        add(u, v, w);        add(v, u, w);    }    scan_d(m);    for(int i = 0; i < m; ++ i) {        scan_d(node[i][0]);node[i][0] --;        scan_d(node[i][1]);node[i][1] --;        addQuery(node[i][0], i);        addQuery(node[i][1], i);    }    father[0] = -1;    tot = 0;    dis[0] = 0;    dfs(0);    for(int i = 0; i < m; ++ i) {        int u = node[i][0];        int v = node[i][1];        int p = lca[i];        printf("%d\n",dis[u] - dis[p] + dis[v] - dis[p]);    }}int main() {//    freopen("data.txt","r",stdin);    solve();    return 0;}

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