LCA倍增算法(模板)

LCA在线倍增模板，模板对应HDU 2586

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define  pb push_back
#define  mp make_pair
#define  sz(x) ((int)(x).size())
using namespace std;

const int N = 40010;
const int INF = (int)1e9;
int fa[N], L[N], n, m, anc[N][33];
int maxcost[N][33], cost[N], que[N * 10];
struct Edge {
    int e, w, next;
}edge[N * 10];
int head[N], cnt = 0, dis[N];

void addedge(int a, int b, int w){
	edge[cnt].e = b;
	edge[cnt].w = w;
	edge[cnt].next = head[a];
	head[a] = cnt++;
}

struct LCA_online {
	void initi(){
	    cnt = cost[1] = L[1] = 0;
	    memset(head, -1, sizeof head);
	}

	void dfs(int u, int f) {
	    fa[u] = f;
	    for(int it = head[u]; ~it; it = edge[it].next) {
	        int v = edge[it].e, w = edge[it].w;
	        if(v != f) {
	            cost[v] = w;
	            L[v] = L[u] + 1;
	            dfs(v, u);
	        }
	    }
	}

	void process() {
		for(int i = 1; i <= n; i++) {
	        anc[i][0] = fa[i], maxcost[i][0] = cost[i];
	        for(int j = 1; (1 << j) < n; j++) anc[i][j] = -1;
	    }
	    for(int j = 1; (1 << j) < n; j++)
			for(int i = 1; i <= n; i++)
	    		if(anc[i][j - 1] != -1) {
	        		int a = anc[i][j - 1];
	        		anc[i][j] = anc[a][j - 1];
	        		maxcost[i][j] = max(maxcost[i][j - 1], maxcost[a][j - 1]);
	    		}
	}
	
	int query(int p, int q) {
	    int lo;
	    if(L[p] < L[q]) swap(p, q);
	    for(lo = 1; (1 << lo) <= L[p]; lo++); lo--;
	    int ans = -INF;
	    for(int i = lo; i >= 0; i--)
	        if(L[p] - (1 << i) >= L[q]) 
				ans = max(ans, maxcost[p][i]), p = anc[p][i];
	    if(p == q)
			return p;	    
//			return ans; //LCA -> p
	    for(int i = lo; i >= 0; i--)
	    	if(anc[p][i] != -1 && anc[p][i] != anc[q][i]) {
	        	ans = max(ans, maxcost[p][i]), p = anc[p][i];
	        	ans = max(ans, maxcost[q][i]), q = anc[q][i];
	    	}
	   	return fa[p];
//    return max(ans, max(cost[p], cost[q])); //LCA -> fa[q] fa[p]
	}
}g;

void bfs() {
	int fr = 0, rear = 0;
 	que[rear++] = 1;
  	dis[1] = 0;
   	while(fr < rear) {
    	int deq = que[fr++];
     	for(int it = head[deq]; ~it;it = edge[it].next	) {
      		int e = edge[it].e, w = edge[it].w;
        	if(dis[e] == -1) {
         		dis[e] = dis[deq] + w;
           		que[rear++] = e;
           	}
		}
  	}
}

int main() {
    int T;
    cin >> T;
    while(T--) {
    	g.initi();
    	memset(dis, -1, sizeof dis);
        cin >> n >> m;
       	for(int i = 0; i < n - 1; i++) {
	    	int a, b, w;
			scanf("%d%d%d", &a, &b, &w);
			addedge(a, b, w);
			addedge(b, a, w);   	
     	}
        g.dfs(1, -1);
        g.process();
        bfs();
        while(m--) {
        	int a, b;
        	scanf("%d%d", &a, &b);
        	int anc = g.query(a, b);
			int ans = dis[a] + dis[b] - dis[anc] * 2;
			printf("%d\n", ans);
        }
    }
    return 0;
}