#include <bits/stdc++.h>
using namespace std;
#define pii pair<int, int>
#define f first
#define s second
int n, m;
vector<pii> pts, sqrs;
map<pii, int> pid, sid;
vector<int> fa, u_ans, v_ans, a_ans, b_ans;
vector<vector<pair<int, pii>>> adj;
vector<bool> vis;
set<pii> roads;
int find(int v){return v==fa[v]?v:fa[v]=find(fa[v]);}
void unite(int u, int v){
u = find(u), v = find(v);
if(u==v) return;
fa[u] = v;
}
pii get(pii a, pii b){
if(a.f==b.f){
if(a.s>b.s) swap(a, b);
int x = pid[{a.f-1, a.s+1}], y = pid[{a.f+1, a.s+1}];
if(x>y) swap(x, y);
return {x, y};
}
if(a.f>b.f) swap(a, b);
int x = pid[{a.f+1, a.s+1}], y = pid[{a.f+1, a.s-1}];
if(x>y) swap(x, y);
return {x, y};
}
bool horz(pii a){
return ((a.f+a.s)/2)&1;
}
void dfs(int v){
vis[v] = 1;
for(auto u : adj[v])
if(!vis[u.f]) roads.erase(u.s), dfs(u.f);
}
int construct_roads(vector<int> _x, vector<int> _y){
n = _x.size();
for(int i = 0; i<n; ++i)
pts.push_back({_x[i], _y[i]}), pid[pts.back()] = i;
fa.resize(n);
iota(fa.begin(), fa.end(), 0);
for(int i = 0; i<n; ++i){
pii npt = {pts[i].f+2, pts[i].s};
if(pid.count(npt)) unite(i, pid[npt]);
npt = {pts[i].f, pts[i].s+2};
if(pid.count(npt)) unite(i, pid[npt]);
}
for(int i = 1; i<n; ++i)
if(find(0)!=find(i)) return 0;
for(int i = 0; i<n; ++i){
pii ap = {pts[i].f+2, pts[i].s}, bp = {pts[i].f, pts[i].s+2};
if(pid.count(ap)) roads.insert({min(i, pid[ap]), max(i, pid[ap])});
if(pid.count(bp)) roads.insert({min(i, pid[bp]), max(i, pid[bp])});
}
for(int i = 0; i<n; ++i){
pii bl = pts[i], br = {bl.f+2, bl.s}, tl = {bl.f, bl.s+2}, tr = {bl.f+2, bl.s+2};
if(pid.count(bl) && pid.count(br) && pid.count(tl) && pid.count(tr))
sqrs.push_back({bl.f+1, bl.s+1}), sid[sqrs.back()] = (int)sqrs.size()-1;
}
m = (int)sqrs.size();
adj.resize(m+1);
vis.assign(m+1, 0);
for(int i = 0; i<m; ++i){
pii as, bs;
if(horz(sqrs[i]))
as = {sqrs[i].f+2, sqrs[i].s}, bs = {sqrs[i].f-2, sqrs[i].s};
else as = {sqrs[i].f, sqrs[i].s+2}, bs = {sqrs[i].f, sqrs[i].s-2};
if(sid.count(as)) adj[i].push_back({sid[as], get(sqrs[i], as)});
if(sid.count(bs)) adj[i].push_back({sid[bs], get(sqrs[i], bs)});
pii cs, ds;
if(((sqrs[i].f+sqrs[i].s)/2)&1)
cs = {sqrs[i].f, sqrs[i].s+2}, ds = {sqrs[i].f, sqrs[i].s-2};
else cs = {sqrs[i].f+2, sqrs[i].s}, ds = {sqrs[i].f-2, sqrs[i].s};
if(!sid.count(cs)) adj[m].push_back({i, get(sqrs[i], cs)});
if(!sid.count(ds)) adj[m].push_back({i, get(sqrs[i], ds)});
} dfs(m);
for(auto [x, y] : roads){
u_ans.push_back(x), v_ans.push_back(y);
pii a = pts[x], b = pts[y];
if(a.f==b.f){
if(a.s>b.s) swap(a, b);
if(horz({a.f-1, a.s+1})) a_ans.push_back(a.f-1), b_ans.push_back(a.s+1);
else a_ans.push_back(a.f+1), b_ans.push_back({a.s+1});
} else{
if(a.f>b.f) swap(a, b);
if(!horz({a.f+1, a.s-1})) a_ans.push_back(a.f+1), b_ans.push_back(a.s-1);
else a_ans.push_back(a.f+1), b_ans.push_back(a.s+1);
}
}
build(u_ans, v_ans, a_ans, b_ans);
return 1;
}
Compilation message
parks.cpp: In function 'int construct_roads(std::vector<int>, std::vector<int>)':
parks.cpp:100:5: error: 'build' was not declared in this scope
100 | build(u_ans, v_ans, a_ans, b_ans);
| ^~~~~
