UVa 11853 PaintBall

#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <list>
#include <stack>
#include <queue>
#include <map>
#include <string>
#include <cctype>
#include <cmath>
#include <cstring>
#include <climits>
#include <complex>
#include <set>
#include <deque>
#define DEBUG(x) cerr<<"line:"<<__LINE__<<", "<<#x" == "<<(x)<<endl;
#define REP(i,s,n) for(int i=(int)(s);i<(int)(n);i++)
#define FOR(it,s) for(__typeof(s.begin()) it=s.begin();it!=s.end();it++)
#define ALL(a) (a).begin(),(a).end()
#define RALL(x) (a).rbegin(),(a).rend()
#define RI(x) scanf("%d",&(x))
#define RII(x,y) scanf("%d%d",&(x),&(y))
#define RIII(x,y,z) scanf("%d%d%d",&(x),&(y),&(z))
#define DRI(x) int (x);scanf("%d",&(x))
#define DRII(x,y) int (x),(y);scanf("%d%d",&(x),&(y))
#define DRIII(x,y,z) int (x),(y),(z);scanf("%d%d%d",&(x),&(y),&(z))
#define MS0(a) memset((a),0,sizeof((a)))
#define MS1(a) memset((a),-1,sizeof((a)))
#define MS(a,b) memset((a),(b),sizeof((a)))
#define PB push_back
#define SZ(a) (int)(a).size()

using namespace std;

typedef long long LL;
typedef unsigned int uint;
typedef unsigned long long ULL;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vii;
typedef vector<vi> vvi;

#define INF 1000000000
const double eps = 1e-10;
int dcmp(double x){
if(fabs(x) < eps) return 0;
else return x < 0 ? -1 : 1;
}
// ------------------
// author : onehrxn
// ------------------
const int maxn = 1000 + 5;
const int TOP = 1000;
const int RIGHT = 1000;
int x[maxn], y[maxn], r[maxn];
vector<int> g[maxn];
bool vis[maxn];
int N;
vector<int> up;
void init(int N);
inline double dis(int a ,int b);
inline bool pinter(int a, int b);
inline bool inter(int p, int dir); // up 0 left 1 down 2 right 3
bool solve(double &ly, double &ry); // return if can be solved and the ans
int main(void)
{
//ios::sync_with_stdio(false);
//cin.tie(0);
#ifdef LOCAL
//freopen("input", "r", stdin);
//freopen("output", "w", stdout);
#endif
while(~RI(N)){
init(N);
for(int i = 0; i < N; i++){
RIII(x[i], y[i], r[i]);
}
for(int i = 0; i < N; i++){
if(inter(i, 0)) up.PB(i);
for(int j = i + 1; j < N; j++)
if(pinter(i,j)){
g[i].PB(j); g[j].PB(i);
}
}
double ly, ry;
if(solve(ly, ry)) {
printf("%.2lf %.2lf %.2lf %.2lf\n", 0.0, ly, 1000.0, ry);
}
else printf("IMPOSSIBLE\n");
}
#ifdef LOCAL
cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
return 0;
}

void init(int N){
up.clear();
for(int i = 0; i < N; i++){
vis[i] = 0;
g[i].clear();
}
}

inline bool pinter(int a, int b){
if(dcmp(dis(a,b) - r[a] - r[b]) <= 0) return 1;
return 0;
}

inline double dis(int a, int b){
return sqrt( (x[b] - x[a])*(x[b] - x[a]) + (y[b] - y[a])*(y[b] - y[a]));
}
inline bool inter(int p, int dir){
switch(dir){
case 0: return ((TOP - y[p]) <= r[p]);
case 1: return ((x[p]) <= r[p]);
case 2: return (y[p] <= r[p]);
case 3: return (RIGHT - x[p] <= r[p]);
}
return 0;
}

bool solve(double &ly, double &ry){
MS0(vis);
queue<int> q;
ly = 1000.0;
ry = 1000.0;
FOR(it, up) q.push(*it);
while(!q.empty()){
int now = q.front(); q.pop();
vis[now] = 1;
if(inter(now, 2)) return 0;
if(inter(now, 1)){
// update the ly
double diffx = x[now] * 1.0;
double tmpy = y[now]*1.0 - (sqrt(r[now]*r[now]*1.0 - diffx*diffx));
if(dcmp(tmpy - ly) < 0) ly = tmpy;
}
if(inter(now, 3)){
// update the ry
double diffx = RIGHT*1.0 - x[now];
double tmpy = y[now]*1.0 - (sqrt(r[now]*r[now]*1.0 - diffx*diffx));
if(dcmp(tmpy - ry) < 0) ry = tmpy;
}
for(int i = 0; i < g[now].size(); i++) {
if(!vis[g[now][i]]) q.push(g[now][i]);
}
}
return 1;
}