POJ 2376
题意：问最少要几个区间才能使区间 [ 1, T ] 全被覆盖掉
1 #include <cstdio> 2 #include <cstring> 3 #include <cstdlib> 4 #include <cctype> 5 #include <cmath> 6 #include <time.h> 7 #include <string> 8 #include <map> 9 #include <stack> 10 #include <set> 11 #include <queue> 12 #include <vector> 13 #include <algorithm> 14 #include <iostream> 15 using namespace std; 16 typedef long long ll; 17 #define PI acos( -1.0 ) 18 const double E = 1e-8; 19 const int INF = 0x7fffffff; 20 21 const int NO = 25000 + 5; 22 int n, t; 23 struct ND 24 { 25 int be, en; 26 }st[NO]; 27 28 bool cmp( const ND &a, const ND &b ) 29 { 30 if( a.be == b.be ) 31 return a.en > b.en; 32 return a.be < b.be; 33 } 34 35 int main() 36 { 37 scanf( "%d%d", &n, &t ); 38 for( int i = 0; i < n; ++i ) 39 scanf( "%d%d", &st[i].be, &st[i].en ); 40 sort( st, st+n, cmp ); 41 int ans = 0; 42 int k = 0; 43 for( int i = 0; i < n; ++i ) 44 { 45 if( k+1 >= st[i].be && st[i].en > k ) 46 { 47 ++ans; 48 int m = st[i].en, j; 49 if( m >= t ) 50 { 51 printf( "%d\n", ans ); 52 return 0; 53 } 54 for( j = i+1; j < n; ++j )//起始时间在k+1中找最大的终止时间 55 if( st[j].be <= k+1 ) 56 { 57 if( m < st[j].en ) 58 m = st[j].en; 59 if( m >= t ) { 60 printf( "%d\n", ans ); 61 return 0; 62 } 63 } else break; 64 k = m; 65 i = j - 1; 66 } 67 else if( k+1 < st[i].be ) 68 break; 69 } 70 puts( "-1" ); 71 return 0; 72 }
