贪心算法 （）

English foundation：

do some cleaning chores

题目：https://cn.vjudge.net/contest/317575#problem/A

Hint:

This problem has huge input data,use scanf() instead of cin to read data to avoid time limit exceed. 

分析：

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;

int n,t;
struct node
{
int a,b;
}q[1<<20];

bool cmp(node x,node y)
{
return x.a<y.a||(x.a==y.a && x.b>y.b);
}

int main()
{
while(~scanf("%d%d",&n,&t))
{
for(int i=0;i<n;i++)
{
scanf("%d%d",&q[i].a,&q[i].b);
}
sort(q,q+n,cmp);

if(q[0].a!=1)
{
puts("-1");
continue;
}

int ans=1;
int r=q[0].b;//r代表已买最右
int nowr=q[0].b;//nowr代表已遍历的最右

for(int i=1;i<n;i++)
{
//出现断点了
if(q[i].a>r+1)
{
r=nowr;
ans++;
}

if(q[i].a<=r+1)
{
if(q[i].b>nowr) nowr=q[i].b;//已遍历的最右

if(q[i].b==t)//不断贪心最右,直至贪到右边界
{
r=t;
ans++;
break;
}
}
}
if(r==t) printf("%d\n",ans);
else puts("-1");
}
return 0;
}

　　

 

 

 

 

 

 

 

 

 

参考：

https://blog.csdn.net/zwj1452267376/article/details/50420633

https://blog.csdn.net/Code92007/article/details/82912887