[Virtual Judge]URAL1303:Minimal Coverage

1
-1 0
-5 -3
2 5
0 0

No solution

1
-1 0
0 1
0 0

1
0 1

=====================================题目大意=====================================

=====================================算法分析=====================================

=======================================代码=======================================

#include<cstdio>
#include<algorithm>

using namespace std;

int M,InterSum,AnsID[100005],CntAns;

struct Interval { int L,R; } Inter[100005];

bool cmp(Interval& I1,Interval& I2)
{
return I1.L<I2.L;
}

bool Greedy()
{
CntAns=0;
sort(Inter,Inter+InterSum,cmp);
int i=0,CurCoverEnd=0;
while(i<InterSum&&CurCoverEnd<M)
{
int Best;
for(Best=-1;i<InterSum;++i)
{
if(Inter[i].R<CurCoverEnd) { continue; }
if(Inter[i].L>CurCoverEnd) { break; }
if(Best==-1||Inter[Best].R<Inter[i].R) { Best=i; }
}
if(Best==-1) { break; }
CurCoverEnd=Inter[Best].R;
AnsID[CntAns++]=Best;
}
return M<=CurCoverEnd;
}

int main()
{
while(scanf("%d",&M)==1)
{
InterSum=0;
while(1)
{
scanf("%d%d",&Inter[InterSum].L,&Inter[InterSum].R);
if(Inter[InterSum].L==0&&Inter[InterSum].R==0) { break; }
++InterSum;
}
if(Greedy()==true)
{
printf("%d\n",CntAns);
for(int i=0;i<CntAns;++i)
{
printf("%d %d\n",Inter[AnsID[i]].L,Inter[AnsID[i]].R);
}
}
else
{
printf("No solution\n");
}
}
return 0;
}