## Editorial for VOI 14 Bài 1 - Con đường Tùng Trúc

Remember to use this editorial only when stuck, and not to copy-paste code from it. Please be respectful to the problem author and editorialist.
Submitting an official solution before solving the problem yourself is a bannable offence.

Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

#### Code mẫu của happyboy99x

#include<algorithm>
#include<vector>
#include<cstdio>
using namespace std;

const int INF = (int) 1e9 + 7;

int main() {
int n, a, b; scanf("%d %d %d", &n, &a, &b);
vector<pair<int, int> > tree (n);
for(int i = 0; i < n; ++i) {
scanf("%d %d", &tree[i].first, &tree[i].second);
}
sort(tree.begin(), tree.end());
vector<int> pos1 (n), pos2 (n);
int x = 0, y = 0, res = INF;
for(int i = 0; i < n; ++i) {
if(tree[i].second == 1) {
pos1[x++] = tree[i].first;
} else {
pos2[y++] = tree[i].first;
}
if(x >= a && y >= b) {
res = min(res, tree[i].first - min(pos1[x - a], pos2[y - b]));
}
}
printf("%d\n", res == INF ? -1 : res);
return 0;
}


program minroad;
uses    math;

type    e=record
x,t:longint;
end;

const   fi      = '';
fo      = '';
maxN    = 300050;

var     a               :array[1..maxN] of e;
truc,tung       :array[0..maxN] of longint;
n,res,p,q       :longint;

procedure input;
var     f:text;
i:longint;
begin
assign(f,fi);
reset(f);
for i:=1 to n do
close(f);
end;

procedure swap(i,j:longint);
var     t:e;
begin
t:=a[i];
a[i]:=a[j];
a[j]:=t;
end;

procedure sort(l,r:longint);
var     p,i,j:longint;
begin
if l>=r then exit;
p:=a[random(r-l+1)+l].x;
i:=l;j:=r;
repeat
while a[i].x<p do inc(i);
while a[j].x>p do dec(j);
if i<=j then
begin
if i<j then swap(i,j);
inc(i);
dec(j);
end;
until i>j;
sort(l,j);sort(i,r);
end;

procedure init;
var     i:longint;
begin
for i:=1 to n do
if a[i].t=1 then
begin
tung[i]:=tung[i-1]+1;
truc[i]:=truc[i-1];
end
else
begin
tung[i]:=tung[i-1];
truc[i]:=truc[i-1]+1;
end;
end;

procedure process;
var     i,j:longint;
begin
res:=high(longint);
j:=2;
for i:=1 to n do
begin
while (j<=n) and (((tung[j]-tung[i-1])<p) or ((truc[j]-truc[i-1])<q)) do
inc(j);
if j<=n then
res:=min(res,a[j].x-a[i].x);
end;
end;

procedure output;
var     f:text;
begin
assign(f,fo);
rewrite(f);
if res=high(longint) then res:=-1;
write(f,res);
close(f);
end;

begin
input;
sort(1,n);
init;
process;
output;
end.


#### Code mẫu của RR

#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; i--)
#define REP(i,a) for(int i=0,_a=(a); i<_a; i++)

#define DEBUG(x) { cout << #x << " = "; cout << x << endl; }
#define PR(a,n) { cout << #a << " = "; FOR(_,1,n) cout << a[_] << ' '; cout << endl; }
#define PR0(a,n) { cout << #a << " = "; REP(_,n) cout << a[_] << ' '; cout << endl; }
using namespace std;

int INP,AM,REACHEOF;
const int BUFSIZE = (1<<12) + 17;
char BUF[BUFSIZE+1], *inp=BUF;
#define GETCHAR(INP) { \
if(!*inp && !REACHEOF) { \
memset(BUF,0,sizeof BUF);\
if (inpzzz != BUFSIZE) REACHEOF = true;\
inp=BUF; \
} \
INP=*inp++; \
}
#define DIG(a) (((a)>='0')&&((a)<='9'))
#define GN(j) { \
AM=0;\
GETCHAR(INP); while(!DIG(INP) && INP!='-') GETCHAR(INP);\
if (INP=='-') {AM=1;GETCHAR(INP);} \
j=INP-'0'; GETCHAR(INP); \
while(DIG(INP)){j=10*j+(INP-'0');GETCHAR(INP);} \
if (AM) j=-j;\
}

const int MN = 300111;
const int oo = 1000111000;

int n, a, b, c1[MN], c2[MN];
pair<int,int> x[MN];

int main() {
ios :: sync_with_stdio(false);
cin >> n >> a >> b;
FOR(i,1,n) cin >> x[i].first >> x[i].second;
sort(x+1, x+n+1);
FOR(i,1,n) {
c1[i] = c1[i-1] + (x[i].second == 1);
c2[i] = c2[i-1] + (x[i].second == 2);
}
int best = oo;
FOR(i,1,n) {
if (c1[i] < a || c2[i] < b) continue;
int left = 1, right = i, res = 1;
while (left <= right) {
int mid = (left + right) >> 1;
if (c1[i] - c1[mid-1] >= a && c2[i] - c2[mid-1] >= b) {
res = mid;
left = mid + 1;
}
else right = mid - 1;
}
best = min(best, x[i].first - x[res].first);
}
if (best == oo) cout << -1; else cout << best;
cout << endl;
return 0;
}