Sicily 2377. Ants Colony

比较经典的LCA问题，如果掌握了Tarjan算法后，这题就很容易地水过了~~

本人在学习Tarjan算法时，参考了ylfdrib的博客：http://www.cnblogs.com/ylfdrib/archive/2010/11/03/1867901.html， 感觉他讲得比较清晰易懂，而且又有相关的代码参考。

 

#include<stdio.h>#include<string.h>#include<vector>#include<algorithm>using namespace std;const int maxn = 100010;const int maxm = 100010;struct node{int v;unsigned long long d;};node tmp;vector<node> g[maxn];vector<node> q[maxn];int p[maxn];int anc[maxn];bool vis[maxn];unsigned long long dis[maxn];unsigned long long res[maxm][3];int n, m;void init(){for(int i = 0; i <= n; i++){p[i] = i;dis[i] = 0;vis[i] = false;anc[i] = i;g[i].clear();q[i].clear();}}int find(int a){return p[a] == a ? a : (p[a] = find(p[a]));}void LCA(int u){anc[u] = u;vis[u] = true;for(int i = 0; i < q[u].size(); i++){tmp = q[u][i];if(vis[tmp.v])res[tmp.d][2] = anc[find(tmp.v)];}for(int i = 0; i < g[u].size(); i++){tmp = g[u][i];int v = tmp.v;if(!vis[v]){dis[v] = dis[u] + tmp.d;LCA(v);int x = find(u);int y = find(v);if(x != y)p[y] = x;anc[x] = u;}}}#define LOCALint main(){#ifdef LOCALfreopen("input.txt", "r", stdin);freopen("output.txt", "w", stdout);#endifwhile(scanf("%d", &n) == 1){if(n == 0)break;init();int a, b;long long c;for(int i = 1; i < n; i++){a = i;scanf("%d%lld", &b, &c);tmp.v = b;tmp.d = c;g[a].push_back(tmp);tmp.v = a;tmp.d = c;g[b].push_back(tmp);}scanf("%d", &m);for(int i = 0; i < m; i++){scanf("%d%d", &a, &b);tmp.v = b;tmp.d = i;q[a].push_back(tmp);tmp.v = a;tmp.d = i;q[b].push_back(tmp);res[i][0] = a;res[i][1] = b;}dis[0] = 0;LCA(0);for(int i = 0; i < m-1; i++)printf("%llu ", dis[res[i][0]] + dis[res[i][1]] - 2*dis[res[i][2]]);printf("%llu/n", dis[res[m-1][0]] + dis[res[m-1][1]] - 2*dis[res[m-1][2]]);}return 0;}