Maratones competidas/Maratón Nacional 2011/workspace/g/gas.cpp

   1 // Equipo Poncho, Carriel y Ruana
   2 using namespace std;
   3 #include <algorithm>
   4 #include <iostream>
   5 #include <iterator>
   6 #include <sstream>
   7 #include <fstream>
   8 #include <cassert>
   9 #include <climits>
  10 #include <cstdlib>
  11 #include <cstring>
  12 #include <string>
  13 #include <cstdio>
  14 #include <vector>
  15 #include <cmath>
  16 #include <queue>
  17 #include <stack>
  18 #include <list>
  19 #include <map>
  20 #include <set>
  21
  22 template <class T> string toStr(const T &x)
  23 { stringstream s; s << x; return s.str(); }
  24 template <class T> int toInt(const T &x)
  25 { stringstream s; s << x; int r; s >> r; return r; }
  26
  27 #define For(i, a, b) for (int i=(a); i<(b); ++i)
  28 #define foreach(x, v) for (typeof (v).begin() x = (v).begin(); x != (v).end(); ++x)
  29 #define D(x) cout << #x " = " << (x) << endl;
  30
  31 const double EPS = 1e-9;
  32
  33 int cmp(double x, double y = 0, double tol = EPS) {
  34     return (x <= y + tol) ? (x + tol < y) ? -1 : 0 : 1;
  35 }
  36
  37 #define INPUT_FILE "gas"
  38
  39
  40 int main(){
  41     freopen(INPUT_FILE ".in", "r", stdin);
  42     long long l, gases;
  43
  44     vector< pair<long long, long long> > stations;
  45
  46     while(cin >> l >> gases) {
  47         bool found = true;
  48         stations.clear();
  49         if(l == 0 and gases == 0) break;
  50         for(long long i=0; i<gases; i++) {
  51             long long p, r;
  52             long long zero = 0;
  53             cin >> p >> r;
  54             long long li, ls;
  55             li = max(zero, p-r);
  56             ls = min(l, p+r);
  57             stations.push_back(make_pair(li, ls));
  58         }
  59         sort(stations.begin(), stations.end());
  60         long long last_index = 0;
  61         long long usados = 0;
  62         for(long long i = 0; i<l;) {
  63             long long fin = i;
  64             bool primero = true;
  65             for(long long g = last_index; g<stations.size(); ++g) {
  66                 if (stations[g].first <= i and stations[g].second > i) {
  67                     if (primero) {
  68                         primero = false;
  69                         last_index = g;
  70                     }
  71                     fin = max(fin, stations[g].second);
  72                 }
  73                 if (stations[g].first > i) break;
  74             }
  75             if(i == fin) {
  76                 cout << -1 << endl;
  77                 found = false;
  78                 break;
  79             }
  80             i = fin;
  81             usados++;
  82         }
  83         if (found) cout << gases-usados << endl;
  84
  85     }
  86     return 0;
  87
  88 }