Distance between two points on the poj 1986 distance queries LCA tree

Source: poj 1986 distance queries

Q: ask you the distance between two points each time in a tree.

Train of Thought: For point 2 u v dis (u, v) = DIS (root, u) + DIS (root, V)-2 * Dis (Roor, LCA (u, v) returns the recent common ancestor and DIS array.

#include <cstdio>#include <cstring>#include <vector>using namespace std;const int maxn = 40010;int first[maxn], head[maxn], cnt, sum;struct edge{int u, v, w, next;}e[maxn*2], qe[maxn], Q[maxn];int ans[maxn];int f[maxn], vis[maxn];int d[maxn];void AddEdge(int u, int v, int w){e[cnt].u = u;e[cnt].v = v;e[cnt].w = w;e[cnt].next = first[u];first[u] = cnt++;e[cnt].u = v;e[cnt].v = u;e[cnt].w = w;e[cnt].next = first[v];first[v] = cnt++;}void AddEdge2(int u, int v, int w){qe[sum].u = u;qe[sum].v = v;qe[sum].w = w;qe[sum].next = head[u];head[u] = sum++;qe[sum].u = v;qe[sum].v = u;qe[sum].w = w;qe[sum].next = head[v];head[v] = sum++;}int find(int x){if(f[x] != x)return f[x] = find(f[x]);return f[x];}void LCA(int u, int k){f[u] = u;d[u] = k;vis[u] = true;for(int i = first[u]; i != -1; i = e[i].next){int v = e[i].v;if(vis[v])continue;LCA(v, k + e[i].w);f[v] = u;}for(int i = head[u]; i != -1; i = qe[i].next){int v = qe[i].v;if(vis[v]){ans[qe[i].w] = find(v);}}} int main(){int n, m;memset(first, -1, sizeof(first));memset(head, -1, sizeof(head));cnt = 0;sum = 0;scanf("%d %d", &n, &m);for(int i = 0; i < m; i++){int u, v, w;char s[10];scanf("%d %d %d %s", &u, &v, &w, s);AddEdge(u, v, w);}int q;scanf("%d", &q);for(int i = 0; i < q; i++){int u, v; scanf("%d %d", &u, &v);Q[i].u = u, Q[i].v = v;AddEdge2(u, v, i);AddEdge2(v, u, i);}memset(vis, 0, sizeof(vis));d[1] = 0;LCA(1, 0);for(int i = 0; i < q; i++){int u = Q[i].u, v = Q[i].v;printf("%d\n", d[u] + d[v] - 2*d[ans[i]]);}return 0;}