过了这么长的时间终于开始看LCA了...
有一次训练题卡在LCA当时不会...拖了好久好久...其实现在还是不会...
只会tarjan...
板子题咯
tarjan的算法就是基于先序遍历的顺序的
#include <bits/stdc++.h> using namespace std; inline int read() { int x = 0, f = 1; char ch = getchar(); while (ch < ‘0‘ || ch > ‘9‘) { if (ch == ‘-‘) f = -1; ch = getchar(); } while (ch >= ‘0‘ && ch <= ‘9‘) { x = x * 10 + ch - ‘0‘; ch = getchar(); } return x * f; } const int maxn = 5e5 + 10; //const int maxm = 8e4 + 10; struct Edge { int to, next, c; } edge[2 * maxn]; int cnt, head[maxn]; struct Qedge { int to, next; } qedge[2 * maxn]; int qcnt, qhead[maxn], n, m; int lca[maxn], dep[maxn], par[maxn]; bool vis[maxn]; inline void addedge(int u, int v, int c) { edge[++cnt].to = v; edge[cnt].c = c; edge[cnt].next = head[u]; head[u] = cnt; } inline void addqedge(int u, int v) { qedge[++qcnt].to = v; qedge[qcnt].next = qhead[u]; qhead[u] = qcnt; } int getfa(int x) { return x == par[x] ? x : par[x] = getfa(par[x]); } void dfs(int u) { par[u] = u; vis[u] = 1; for (int i = head[u]; i; i = edge[i].next) { int v = edge[i].to; if (!vis[v]) { dep[v] = dep[u] + edge[i].c; dfs(v); par[v] = u; } } for (int i = qhead[u]; i; i = qedge[i].next) { int v = qedge[i].to; if (vis[v]) { lca[i] = getfa(v); if (i % 2) lca[i + 1] = lca[i]; else lca[i-1] = lca[i]; } } } int main() { n = read(); for (int i = 0; i < n - 1; i++) { int u = read(), v =read(), c = read(); addedge(u, v, c); addedge(v, u, c); } m = read(); for (int i = 0; i < m; i++) { int u = read(), v = read(); addqedge(u, v); addqedge(v, u); } dfs(0); for (int i = 1; i <= m; i++) { int ans = dep[qedge[2 * i].to] - 2 * dep[lca[2 * i]] + dep[qedge[2 * i - 1].to]; printf("%d\n", ans); } return 0; }
原文地址:https://www.cnblogs.com/Mrzdtz220/p/10777225.html
时间: 2024-10-10 06:46:47