Submission #743606

#	Time	Username	Problem	Language	Result	Execution time	Memory
743606		RushB	Swapping Cities (APIO20_swap)	C++17	0 / 100	397 ms	48460 KiB

swap

//happier ending for folks like us? 
#include "swap.h"
#include <bits/stdc++.h>
using namespace std;
const int N = 4e5 + 15;
const int M = 2e5 + 5;
const int L = 21;
int p[N], dpr[N], pr[N][L], ext[N], P[N], h[N], rt, D[N], deg[N];
vector<int> adj[N], Wtmp;

void smin(int &a, int b) {a = min(a, b);}

void dfs(int v) {
	for (int i = 1; i < L; i++) pr[v][i] = pr[pr[v][i - 1]][i - 1];
	for (auto u: adj[v]) {
		pr[u][0] = v;
		h[u] = h[v] + 1;
		dfs(u);
		smin(ext[v], ext[u]);
		P[v] = max(P[v], P[u]);
	}
	P[v] = max(P[v], (int) adj[v].size());
}
void add_edge(int u, int e) {
	adj[e].push_back(u);
}

int gpr(int u) {
	return dpr[u] == u ? u : dpr[u] = gpr(dpr[u]);
}

bool merge(int u, int v, int id) {
	int tu = u, tv = v;
	deg[tu]++, deg[tv]++;
	u = gpr(u), v = gpr(v);
	if (u == v) return false;
	dpr[u] = id + M;
	dpr[v] = id + M;
	D[id + M] = max({D[u], D[v], deg[tu], deg[tv]});
	add_edge(u, id + M);
	add_edge(v, id + M);
	return true;
}

void init(int n, int m, std::vector<int> U, std::vector<int> V, std::vector<int> W) {
	iota(p, p + m, 0);
	sort(p, p + m, [&](const int x, const int y) {return W[x] < W[y];});
	iota(dpr, dpr + N, 0);

	memset(ext, 0x3f3f3f, sizeof ext);
	Wtmp = W;
	
	for (int i = 0; i < m; i++) {
		const int id = p[i];
		if (!merge(U[id], V[id], id)) {
			smin(ext[U[id]], W[id]);
			smin(ext[V[id]], W[id]);
		}
	}
	rt = gpr(0);
	pr[rt][0] = rt;
	dfs(rt);
}

int getMinimumFuelCapacity(int X, int Y) {
	if (h[X] < h[Y]) swap(X, Y);
	while (h[Y] < h[X]) X = pr[X][__lg(h[X] - h[Y])];
	assert(Y != X);
	for (int i = L - 1; i >= 0; i--) if (pr[Y][i] != pr[X][i]) 
		Y = pr[Y][i], X = pr[X][i];
	assert(pr[X][0] == pr[Y][0]);
	int lca = pr[X][0], l = lca - M, w = Wtmp[l], p = P[lca];

	if (D[lca] > 2) return w;
	w = max(w, ext[lca]);
	return w > M ? -1 : w;
}

Compilation message (stderr)

swap.cpp: In function 'int getMinimumFuelCapacity(int, int)':
swap.cpp:72:48: warning: unused variable 'p' [-Wunused-variable]
   72 |  int lca = pr[X][0], l = lca - M, w = Wtmp[l], p = P[lca];
      |                                                ^

• Subtask 1: 0 / 6
• Subtask 2: 0 / 7
• Subtask 3: 0 / 17
• Subtask 4: 0 / 20
• Subtask 5: 0 / 23
• Subtask 6: 0 / 27