LCA模板整理

Posted 2020-12-31 wwkkk

HDU2586 纯LCA模板

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#define lowbit(x) x&(-x)
#define rep(i,l,r) for(int i=l;i<=r;++i)
#define per(i,r,l) for(int i=r;i>=l;--i)
#define ls o<<1
#define rs o<<1|1
#define lson L,mid,ls
#define rson mid+1,R,rs
#define fi first
#define se second
using namespace std;
inline char nc() {
    static char buf[100000], *p1 = buf, *p2 = buf;
    return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 100000, stdin), p1 == p2) ? EOF : *p1++;
}
inline int _read() {
    char ch = nc(); int sum = 0;
    while (!(ch >= ‘0‘&&ch <= ‘9‘))ch = nc();
    while (ch >= ‘0‘&&ch <= ‘9‘)sum = sum * 10 + ch - 48, ch = nc();
    return sum;
}

typedef long long ll;
const int maxn = 4e4+10;
const double eps = 1e-8;
const int mod = 998244353;
const double pi = acos(-1.0);

vector<pair<int,int>> G[maxn];
int dep[maxn],dis[maxn],par[maxn][20];

void dfs(int u,int fa,int dp,int ds)
{
    dep[u]=dp;
    dis[u]=ds;
    if(u==1)
    {
        for(int i=0;i<20;i++)par[u][i]=1;
    }
    else
    {
        par[u][0]=fa;
        for(int i=1;i<20;i++)
        {
            par[u][i]=par[par[u][i-1]][i-1];
        }
    }
    for(auto e:G[u])
    {
        int v=e.fi,c=e.se;
        if(v==fa) continue;
        dfs(v,u,dp+1,ds+c);
    }
}

int Jump(int u,int ds)
{
    for(int j=19;j>=0;j--)
    {
        if((1<<j)&ds)
        {
            u=par[u][j];
        }
    }
    return u;
}

int lca(int u,int v)
{
    if(dep[u]<dep[v]) swap(u,v);
    //u 深度较大
    u=Jump(u,dep[u]-dep[v]);
    if(u==v) return u;
    for(int i=19;i>=0;i--)
    {
        if(par[u][i]!=par[v][i])
        {
            u=par[u][i];
            v=par[v][i];
        }
    }
    return par[u][0];
}


int main()
{
    int T;
    T=_read();
    while(T--)
    {
        int n,m;
        n=_read(),m=_read();
        for(int i=1;i<n;i++)
        {
            int u,v,c;
            u=_read(),v=_read(),c=_read();
            G[u].push_back(make_pair(v,c));
            G[v].push_back(make_pair(u,c));
        }
        dfs(1,1,0,0);
        for(int i=1;i<=m;i++)
        {
            int u,v;
            u=_read(),v=_read();
            int ca=lca(u,v);
            printf("%d
",dis[u]+dis[v]-2*dis[ca]);
        }
    }
}

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