Submission #758401

#	Time	Username	Problem	Language	Result	Execution time	Memory
758401		yellowtoad	Swapping Cities (APIO20_swap)	C++17	0 / 100	163 ms	76588 KiB

swap

#include "swap.h"
#include <iostream>
#include <vector>
#include <algorithm>
#define f first
#define s second
using namespace std;

int n, m, freq[100010], p[100010], id[100010], par[300010][20], depth[300010];
bool can[300010];
pair<int,pair<int,int>> ed[200010];
vector<int> edge[300010];

int dsu(int u) {
    if (p[u] == u) return u;
    return (p[u] = dsu(p[u]));
}

void dfs(int u, int d) {
    int v = par[u][0];
    depth[u] = d;
    for (int i = 1; i <= 19; i++) {
        par[u][i] = par[v][i-1];
        v = par[u][i];
    }
    for (int i = 0; i < edge[u].size(); i++) dfs(edge[u][i],d+1);
}

int lca(int u, int v) {
    if (depth[v] < depth[u]) swap(u,v);
    int i = 19;
    while (depth[v] != depth[u]) {
        if (depth[par[v][i]] >= depth[u]) v = par[v][i];
        i--;
    }
    if (v == u) return u;
    while (i >= 0) {
        if (par[v][i] != par[u][i]) {
            u = par[u][i];
            v = par[v][i];
        }
        i--;
    }
    return par[u][0];
}

void init(int N, int M, std::vector<int> U, std::vector<int> V, std::vector<int> W) {
    n = N; m = M;
    for (int i = 0; i < m; i++) ed[i] = {W[i],{U[i],V[i]}};
    sort(ed,ed+m);
    for (int i = 0; i < n; i++) p[i] = id[i] = i;
    for (int i = 0; i < m; i++) {
        int u = ed[i].s.f, v = ed[i].s.s, w = ed[i].f;
        if (dsu(u) == dsu(v)) {
            par[id[dsu(u)]][0] = n+i;
            edge[n+i].push_back(id[dsu(u)]);
            id[dsu(u)] = n+i;
            freq[u]++;
            freq[v]++;
            can[n+i] = 1;
        } else {
            par[id[dsu(u)]][0] = n+i;
            par[id[dsu(v)]][0] = n+i;
            edge[n+i].push_back(id[dsu(u)]);
            edge[n+i].push_back(id[dsu(v)]);
            freq[u]++;
            freq[v]++;
            if ((freq[u] >= 3) || (freq[v] >= 3) || (can[id[dsu(u)]]) || (can[id[dsu(v)]])) can[n+i] = 1;
            p[dsu(v)] = p[dsu(u)];
            id[dsu(u)] = n+i;
        }
    }
    dfs(n+m-1,1);
    can[0] = 1;
}

int getMinimumFuelCapacity(int U, int V) {
    int u = lca(U,V);
    if (can[u]) return ed[u-n].f;
    int i = 19;
    while (i >= 0) {
        if (!can[par[u][i]]) u = par[u][i];
        i--;
    }
    if (!par[u][0]) return -1;
    return ed[par[u][0]-n].f;
}

Compilation message (stderr)

swap.cpp: In function 'void dfs(int, int)':
swap.cpp:26:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   26 |     for (int i = 0; i < edge[u].size(); i++) dfs(edge[u][i],d+1);
      |                     ~~^~~~~~~~~~~~~~~~
swap.cpp: In function 'void init(int, int, std::vector<int>, std::vector<int>, std::vector<int>)':
swap.cpp:53:43: warning: unused variable 'w' [-Wunused-variable]
   53 |         int u = ed[i].s.f, v = ed[i].s.s, w = ed[i].f;
      |                                           ^

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