UVALive 2322 Wooden Sticks sorting + greedy

Give the first and tail coordinates of n wooden bars, and find the minimum number of non-descending sequence of wooden bars. After sorting, simulate it. Code:

 /*  *   Author:        illuz <iilluzen[at]gmail.com>  *   Blog:          http://blog.csdn.net/hcbbt  *   File:          uvalive2322.cpp  *   Lauguage:      C/C++  *   Create Date:   2013-09-06 20:50:20  *   Descripton:    greedy, sort   */  #include <cstdio>  #include <cstring>  #include <algorithm>  using namespace std;  #define rep(i, n) for (int i = 0; i < (n); i++)  #define mc(a) memset(a, 0, sizeof(a))    const int MAXN = 5001;  struct P {      int lhs, rhs;  } p[MAXN];  int t, n;  bool vis[MAXN];    bool cmp(P a, P b) {      if (a.lhs != b.lhs) return a.lhs < b.lhs;      else return a.rhs < b.rhs;  }    int main() {      scanf("%d", &t);      while (t--) {          // input          scanf("%d", &n);          rep(i, n) scanf("%d%d", &p[i].lhs, &p[i].rhs);          // sort          sort(p, p + n, cmp);          // solve          mc(vis);          int cnt = 0;          while (1) {              int i;              for (i = 0; i < n; i++)                  if (!vis[i]) break;              if (i == n) break;              vis[i] = true;              int l = p[i].lhs, r = p[i].rhs;              for (i++; i < n; i++)                  if (!vis[i] && p[i].lhs >= l && p[i].rhs >= r) {                      vis[i]++;                      l = p[i].lhs;                      r = p[i].rhs;                  }              cnt++;          }          printf("%d\n", cnt);      }      return 0;  }