POJ 2763 在线lca

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链接：http://poj.org/problem?id=2763

题意：n个点构成树，q个询问，每次询问得到树上两点距离。

操作一：问从当前位置（起始在s）到v的距离（每次移动到新的地方）。

操作二：将第i条边的长度改为w

处理出到树根的距离，操作一每次用lca求dis[s] + dis[t] - 2*dis[lca(s,t)]；操作二，更新某条边之后对这条边下面的子树到树根的距离更新。

代码：

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <vector>#include <queue>#include <set>#include <map>#include <string>#include <cmath>#include <cstdlib>#include <ctime>#include <stack>using namespace std;#define mem(a,b) memset((a),(b),sizeof((a)))#define For(i,a,b) for(int (i)=(a);(i) < (b);(i)++)#define Ror(i,a,b) for(int (i)=(a);(i) > (b);(i)--)#define mp make_pair#define pb push_back#define inf 0x3f3f3f3fvoid RI (int& x){    x = 0;    char c = getchar ();    while (c == ' '||c == '\n')    c = getchar ();    bool flag = 1;    if (c == '-'){        flag = 0;        c = getchar ();    }    while (c >= '0' && c <= '9'){        x = x * 10 + c - '0';        c = getchar ();    }    if (!flag)    x = -x;}void RII (int& x, int& y){RI (x), RI (y);}void RIII (int& x, int& y, int& z){RI (x), RI (y), RI (z);}const int maxn = 200010;const int maxm = 200010;struct Side {    int v,w,next;}side[maxm];int top,node[maxn];void add_side(int u,int v,int w){    side[top] = (Side){v,w,node[u]};    node[u] = top++;}int ver[maxn];int r_min[maxn][20];int first[maxn],dis[maxn],R[maxn];//R深度int tt;void ST(int n){    for(int i=1;i<=n;i++){        r_min[i][0]=i;    }    int k=log((double)(n+1))/log(2.0);    for(int j=1;j<=k;j++){        for(int i=1;i+(1<<j)-1<=n;i++){            int a = r_min[i][j-1],b = r_min[i+(1<<(j-1))][j-1];            r_min[i][j] = R[a] < R[b] ? a : b;        }    }}int RMQ(int l,int r){    int k=log((double)(r-l+1))/log(2.0);    int a = r_min[l][k],b = r_min[r-(1<<k)+1][k];    return R[a] < R[b] ? a : b;}int lca(int a,int b){    a = first[a];    b = first[b];    if(a > b)swap(a,b);    int ans = RMQ(a,b);    return ver[ans];}void dfs(int u,int dep){    ver[++ tt] = u;first[u] = tt;R[tt] = dep;    for(int i = node[u];i != -1;i = side[i].next){        int v = side[i].v;        if(first[v] == 0){            dis[v] = dis[u] + side[i].w;            dfs(v,dep+1);            ver[++ tt] = u;R[tt] = dep;        }    }}struct BB{    int s,t;}bb[maxm];void do_chg(int ss,int fa,int cc){    dis[ss] += cc;    for(int i = node[ss];i != -1;i = side[i].next){        int v = side[i].v;        if(v != fa)do_chg(v,ss,cc);    }}void change(int fa,int son,int w){    if(dis[fa] > dis[son])swap(fa,son);//cout<<fa<<' '<<son<<endl;    int cc;    for(int i = node[fa];i != -1;i = side[i].next){        int v = side[i].v;        if(v == son){            cc = w - side[i].w;            side[i].w = w;            break;        }    }    do_chg(son,fa,cc);}int main(){    //freopen("test.txt","r",stdin);    int n,q,s;    while(~scanf("%d%d%d",&n,&q,&s)){        mem(node,-1);top = 0;        For(i,0,n-1){            int a,b,c;            RIII(a,b,c);            add_side(a,b,c);            add_side(b,a,c);            bb[i+1] = (BB){a,b};        }        mem(first,0);        tt = 0;dis[1] = 0;        dfs(1,1);        ST(2*n-1);        while(q --){            int op;            RI(op);            switch(op){                case 0:{                    int t;                    RI(t);                    cout<<dis[s] + dis[t] - 2*dis[lca(s,t)]<<endl;                    //cout<<"fa:"<<lca(first[s],first[t])<<endl;                    s = t;                    break;                }                case 1:{                    int i,w;                    RII(i,w);                    change(bb[i].s,bb[i].t,w);                    break;                }            }        }    }    return 0;}

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