Submission #288509

#	Time	Username	Problem	Language	Result	Execution time	Memory
288509		shayan_p	Towns (IOI15_towns)	C++17	100 / 100	29 ms	896 KiB

towns

#include<bits/stdc++.h>
#include "towns.h"

#define F first
#define S second
#define PB push_back
#define sz(s) (int(s.size()))
#define bit(n, k) (((n)>>(k))&1)

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef long double ld;

const int maxn = 1e5 + 10, mod = 1e9 + 7, inf = 1e9 + 7;

int n;
int ds[2][maxn], h[maxn], D[maxn];

int far(int u, int o){
    ds[o][u] = 0;
    for(int i = 0; i < n; i++){
	if(i != u)
	    ds[o][i] = getDistance(u, i);
    }
    int mx = 0;
    for(int i = 0; i < n; i++){
	if(ds[o][mx] < ds[o][i])
	    mx = i;
    }
    return mx;
}
bool same(int a, int b){
    return getDistance(a, b) < h[a] + h[b];
}

int par[maxn];

int fnd(int u){
    return par[u] < 0 ? u : par[u] = fnd(par[u]);
}
void mrg(int a, int b){
    if((a = fnd(a)) == (b = fnd(b)))
	return;
    par[a]+= par[b];
    par[b] = a;
}

int hubDistance(int n, int sub){
    fill(par, par + n, -1);
    ::n = n;
    int A = far(0, 0);
    int B = far(A, 1);
    int TR = ds[1][B];
    int TR2 = ds[0][A];
    
    int R = inf;
    map<int, int> mp;
    for(int i = 0; i < n; i++){
	h[i] = (ds[0][i] + ds[1][i] - TR2) / 2;
	D[i] = ds[1][i] - h[i];
	R = min(R, max(D[i], TR - D[i]));
	mp[D[i]]++;
    }
    
    int sm = 0;
    vector<pii> Ds;    
    for(pii p : mp){
	sm+= p.S;
	if(max(p.F, TR - p.F) == R){
	    Ds.PB({p.F, sm});
	}
    }
    assert(!Ds.empty());
    assert(sz(Ds) <= 2);
    int bstD = Ds[0].F;
    if(sz(Ds) == 2){
	int A = Ds[0].S, B = n - Ds[0].S;
	if(A < B)
	    bstD = Ds[1].F;
    }
    sm = 0;
    for(pii p : mp){
	if(p.F < bstD)
	    sm+= p.S;
    }
    if(sm + sm > n)
	return -R;
    sm = 0;
    for(pii p : mp){
	if(p.F > bstD)
	    sm+= p.S;
    }
    if(sm + sm > n)
	return -R;

    if(mp[bstD] * 2 <= n)
	return R;

    int U = -1, CNT = 0;
    for(int i = 0; i < n; i++){
	if(D[i] == bstD){
	    if(CNT == 0 || same(U, i)){
		if(CNT == 0)
		    U = i;
		else
		    mrg(U, i);
		CNT++;
	    }
	    else{
		CNT--;
	    }
	}
    }
    if(CNT == 0)
	return R;
    CNT = -par[ fnd(U) ];
    for(int i = 0; i < n; i++){
	if(D[i] == bstD && fnd(i) == i && fnd(i) != fnd(U) && same(U, i)){
	    CNT+= -par[ fnd(i) ];
	}	    
    }
    if(CNT + CNT > n)
	return -R;
    return R;
}

Compilation message (stderr)

towns.cpp: In function 'int hubDistance(int, int)':
towns.cpp:50:31: warning: declaration of 'n' shadows a global declaration [-Wshadow]
   50 | int hubDistance(int n, int sub){
      |                               ^
towns.cpp:18:5: note: shadowed declaration is here
   18 | int n;
      |     ^
towns.cpp:79:6: warning: declaration of 'A' shadows a previous local [-Wshadow]
   79 |  int A = Ds[0].S, B = n - Ds[0].S;
      |      ^
towns.cpp:53:9: note: shadowed declaration is here
   53 |     int A = far(0, 0);
      |         ^
towns.cpp:79:19: warning: declaration of 'B' shadows a previous local [-Wshadow]
   79 |  int A = Ds[0].S, B = n - Ds[0].S;
      |                   ^
towns.cpp:54:9: note: shadowed declaration is here
   54 |     int B = far(A, 1);
      |         ^
towns.cpp:50:28: warning: unused parameter 'sub' [-Wunused-parameter]
   50 | int hubDistance(int n, int sub){
      |                        ~~~~^~~

• Subtask 1: 13 / 13
• Subtask 2: 12 / 12
• Subtask 3: 13 / 13
• Subtask 4: 10 / 10
• Subtask 5: 13 / 13
• Subtask 6: 39 / 39