贪心 URAL 1303 Minimal Coverage

题目传送门

 /*
     题意：最少需要多少条线段能覆盖[0, m]的长度
     贪心：首先忽略被其他线段完全覆盖的线段，因为选取更长的更优
             接着就是从p=0开始，以p点为标志，选取 (node[i].l <= p && p < node[i+1].l)
     详细解释：http://www.cnblogs.com/freezhan/p/3219046.html
 */
 #include <cstdio>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 using namespace std;

 const int MAXN = 1e6 + ;
 const int INF = 0x3f3f3f3f;
 struct Node
 {
     int l, r;
 }node[MAXN], ans[MAXN];

 bool cmp(Node x, Node y)
 {
     if (x.l == y.l)    return x.r > y.r;
     else    return x.l < y.l;
 }

 int main(void)        //URAL 1303 Minimal Coverage
 {
     //freopen ("R.in", "r", stdin);

     int m;
     while (scanf ("%d", &m) == )
     {
         int n = ;    int u, v;
         while (scanf ("%d%d", &u, &v) ==  && (u || v))
             node[++n].l = u, node[n].r = v;
         sort (node+, node++n, cmp);

         int k = ;
         for (int i=; i<=n; ++i)        //cover
         {
             if (node[k].l < node[i].l && node[k].r < node[i].r)
             {
                 node[++k] = node[i];
             }
         }

         n = k;    int p = ;    int cnt = ;
         node[n+].l = node[n+].r = m + ;
         for (int i=; i<=n; ++i)
         {
             if (node[i].l <= p && p < node[i+].l)
             {
                 ans[++cnt] = node[i];    p = node[i].r;
             }
             if (p >= m)
             {
                 printf ("%d\n", cnt);
                 for (int i=; i<=cnt; ++i)
                 {
                     printf ("%d %d\n", ans[i].l, ans[i].r);
                 }
                 break;
             }
         }

         if (p < m)    puts ("No solution");
     }

     return ;
 }

 /*
 No solution
 */