Submission #1871897

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Source Code Expand

#define _USE_MATH_DEFINES
#include <iostream>
#include <fstream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <string>
#include <vector>
#include <utility>
#include <complex>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <deque>
#include <tuple>
#include <bitset>
#include <algorithm>
#include <random>
using namespace std;
typedef long double ld;
typedef long long ll;
typedef vector<int> vint;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef complex<ld> compd;
#define reach(i,a)	for(auto i:a)
#define rep(i,n)	for(int i=0;i<n;i++)
#define srep(i,a,n)	for(int i=a;i<n;i++)
#define REP(i,n)	for(int i=0;i<=n;i++)
#define SREP(i,a,n)	for(int i=a;i<=n;i++)
#define rrep(i,n)	for(int i=n-1;i>=0;i--)
#define RREP(i,n)	for(int i=n;i>=0;i--)
#define all(a)	(a).begin(),(a).end()
#define mp(a,b)	make_pair(a,b)
#define mt	make_tuple
#define pb	push_back
#define fst	first
#define scn second
int bitcnt(ll x) {
	x = ((x & 0xAAAAAAAAAAAAAAAA) >> 1) + (x & 0x5555555555555555);
	x = ((x & 0xCCCCCCCCCCCCCCCC) >> 2) + (x & 0x3333333333333333);
	x = ((x & 0xF0F0F0F0F0F0F0F0) >> 4) + (x & 0x0F0F0F0F0F0F0F0F);
	x = ((x & 0xFF00FF00FF00FF00) >> 8) + (x & 0x00FF00FF00FF00FF);
	x = ((x & 0xFFFF0000FFFF0000) >> 16) + (x & 0x0000FFFF0000FFFF);
	x = ((x & 0xFFFFFFFF00000000) >> 32) + (x & 0x00000000FFFFFFFF);
	return x;
}
int bitcnt(int x) {
	x = ((x & 0xAAAAAAAA) >> 1) + (x & 0x55555555);
	x = ((x & 0xCCCCCCCC) >> 2) + (x & 0x33333333);
	x = ((x & 0xF0F0F0F0) >> 4) + (x & 0x0F0F0F0F);
	x = ((x & 0xFF00FF00) >> 8) + (x & 0x00FF00FF);
	x = ((x & 0xFFFF0000) >> 16) + (x & 0x0000FFFF);
	return x;
}
ll gcd(ll a, ll b) {
	return a%b == 0 ? b : gcd(b, a%b);
}
#define debug(x)	cout<<"case #" << x << ": " << endl
#define DEBUG 0
const ll inf = (ll)1e9;
const ll mod = 1e9 + 7;
const ld eps = 1e-9;
const int dx[] = { 0,1,0,-1 };
const int dy[] = { 1,0,-1,0 };

vector<pii> edge[100000];
// LCA用。parent[i][j]:頂点iの2^j個上の点
int parent[100000][20];
// 木の深さ
int depth[100000];
// 同時に用いる辺の最大の重み
int maxm[100000][20];

// Union Find
int group[100000];
int findgroup(int i) {
	return group[i] == i ? i : group[i] = findgroup(group[i]);
}
void merge(int a, int b) {
	a = findgroup(a);
	b = findgroup(b);
	group[a] = b;
}

// LCAの最初の段階。木に対して、1つ上の親を決める
void dfs(int cur, int p, int e) {
	depth[cur] = depth[p] + 1;
	parent[cur][0] = p;
	maxm[cur][0] = e;
	reach(v, edge[cur]) {
		if (v.first != p)	dfs(v.first, cur, v.second);
	}
}

int main() {
	int n, m;	cin >> n >> m;
	rep(i, n)	group[i] = i;
	// 辺を追加して閉路が出来る（＝グループが既に同じ）なら無視してよい
	rep(i, m) {
		int a, b;	cin >> a >> b;	a--;	b--;
		if (findgroup(a) != findgroup(b)) {
			merge(a, b);
			edge[a].push_back(mp(b, i + 1));
			edge[b].push_back(mp(a, i + 1));
		}
	}
	// dfsを行い、木の順序を確定とともに、parent[i][0]=1つ上の親を確定
	rep(i, n)	rep(j, 20) {
		parent[i][j] = i;	maxm[i][j] = -1;
	}
	rep(i, n) {
		if (parent[i][0] == i) {
			dfs(i, i, m + 1);
		}
	}
	// parentの確定を行う
	srep(t, 1, 20) {
		rep(i, n) {
			parent[i][t] = parent[parent[i][t - 1]][t - 1];
			maxm[i][t] = max(maxm[i][t - 1], maxm[parent[i][t - 1]][t - 1]);
		}
	}
	int q;	cin >> q;
	rep(t, q) {
		int x, y;	cin >> x >> y;	x--;	y--;
		// 木が違います
		if (findgroup(x) != findgroup(y)) {
			cout << -1 << endl;
		}
		else {
			// LCAしながらretを下げていく
			int ret = -1;
			// 高さ合わせ
			while (depth[x] > depth[y]) {
				int j = 0;
				while (depth[parent[x][j + 1]] > depth[y])	j++;
				ret = max(ret, maxm[x][j]);
				x = parent[x][j];
			}
			while (depth[y] > depth[x]) {
				int j = 0;
				while (depth[parent[y][j + 1]] > depth[x]) j++;
				ret = max(ret, maxm[y][j]);
				y = parent[y][j];
			}
			// 同時に上っていきます
			while (x != y) {
				int j = 0;
				while (parent[x][j + 1] != parent[y][j + 1])	j++;
				ret = max(ret, max(maxm[x][j], maxm[y][j]));
				x = parent[x][j];
				y = parent[y][j];
			}
			cout << ret << endl;
		}
	}
}

Submission Info

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