제출 #246586

#	제출 시각UTC-0	아이디	문제	언어	결과	실행 시간	메모리
246586	2020-07-09 16:19:50	santaclaus03	Railway (BOI17_railway)	C++14	100 / 100	378 ms	43760 KiB

railway

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#include <bits/stdc++.h>
using namespace std;
using ii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
int n, m, k; 
vvi tree, anc;
vi discovery, finish, v, ans;
map<ii, int> edge_idx;
int t = 0;
void pre(int u, int p) {
    discovery[u] = t++;
    anc[u][0] = p;
    for (int i = 1; i < 20; ++i) anc[u][i] = anc[anc[u][i - 1]][i - 1];
    for (int v : tree[u]) if (v != p) pre(v, u);
    finish[u] = t++;
}
bool is_anc(int a, int b) {
    return discovery[a] <= discovery[b] && finish[b] <= finish[a];
}
int lca(int a, int b) {
    if (is_anc(a, b)) return a;
    if (is_anc(b, a)) return b;
    for (int step = 19; step >= 0; --step) {
        if (!is_anc(anc[a][step], b)) a = anc[a][step];
    }
 
 
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