【tarjan】17.6.1 仙人球 题解

xiaoxiao2021-02-28  8

#include <cstdio> #include <algorithm> #define N 200010 using namespace std; int head[N][2] , to[N][2] , next1[N][2] , cnt[2] , dd[N] , low[N] , tot , vis[N] , ins[N] , sta[N] , top , bel[N] , num; int fa[N][22] , deep[N] , sum[N][22] , log1[N] , pow1[N]; void add(int p , int x , int y) { to[++cnt[p]][p] = y , next1[cnt[p]][p] = head[x][p] , head[x][p] = cnt[p]; } void tarjan(int x , int from) { int i , t; dd[x] = low[x] = ++tot , vis[x] = ins[x] = 1 , sta[++top] = x; for(i = head[x][0] ; i ; i = next1[i][0]) { if(to[i][0] == from) continue; if(!vis[to[i][0]]) tarjan(to[i][0] , x) , low[x] = min(low[x] , low[to[i][0]]); else if(ins[to[i][0]]) low[x] = min(low[x] , dd[to[i][0]]); } if(dd[x] == low[x]) { num ++ ; do { t = sta[top -- ] , ins[t] = 0 , bel[t] = num; if(t != x) sum[num][0] = 1; }while(t != x); } } void dfs(int x) { int i; for(i = 1 ; i <= log1[deep[x]] ; i ++ ) fa[x][i] = fa[fa[x][i - 1]][i - 1] , sum[x][i] = sum[x][i - 1] + sum[fa[x][i - 1]][i - 1]; for(i = head[x][1] ; i ; i = next1[i][1]) if(to[i][1] != fa[x][0]) fa[to[i][1]][0] = x , deep[to[i][1]] = deep[x] + 1 , dfs(to[i][1]); } int cal(int x , int y) { int i , ans = 0; if(deep[x] < deep[y]) swap(x , y); for(i = log1[deep[x] - deep[y]] ; i >= 0 ; i -- ) if(deep[x] - deep[y] >= (1 << i)) ans += sum[x][i] , x = fa[x][i]; for(i = log1[deep[x]] ; i >= 0 ; i -- ) if(fa[x][i] != fa[y][i]) ans += sum[x][i] + sum[y][i] , x = fa[x][i] , y = fa[y][i]; if(x != y) ans += sum[x][0] + sum[y][0] , x = fa[x][0]; return ans + sum[x][0]; } int main() { freopen("cactus.in","r",stdin); freopen("cactus.out","w",stdout); int n , m , k , i , x , y; scanf("%d%d" , &n , &m); while(m -- ) scanf("%d%d" , &x , &y) , add(0 , x , y) , add(0 , y , x); tarjan(1 , 0); for(x = 1 ; x <= n ; x ++ ) for(i = head[x][0] ; i ; i = next1[i][0]) if(bel[x] != bel[to[i][0]]) add(1 , bel[x] , bel[to[i][0]]); pow1[0] = 1 , pow1[1] = 2; for(i = 2 ; i <= n ; i ++ ) log1[i] = log1[i >> 1] + 1 , pow1[i] = pow1[i - 1] * 2 % 1000000007; dfs(1); scanf("%d" , &k); while(k -- ) scanf("%d%d" , &x , &y) , printf("%d\n" , pow1[cal(bel[x] , bel[y])]); fclose(stdin); fclose(stdout); return 0; }