Interval problem AcWing 906. Interval grouping

Original link

AcWing 906. Interval grouping

Algorithm tags

greedy

Ideas

ans Minimum number of groups , The correct answer
cnt The legal scheme is obtained according to the following algorithm
so ans<=cnt

prove ans>=cnt

therefore ans==cnt

Code

#include<bits/stdc++.h>
#define int long long
#define rep(i, a, b) for(int i=a;i<b;++i)
#define Rep(i, a, b) for(int i=a;i>b;--i)
using namespace std;
const int N = 100005;
inline int read(){
   int s=0,w=1;
   char ch=getchar();
   while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
   while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
   return s*w;
}
void put(int x) {
    if(x<0) putchar('-'),x=-x;
    if(x>=10) put(x/10);
    putchar(x%10^48);
}
struct Sec{
    int l, r;
}sec[N];
int mxr[N];
bool cmp(Sec A, Sec B){
    return A.l<B.l;
}
signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int n=read();
	rep(i, 0, n){
	    sec[i].l=read(), sec[i].r=read();
	}
	sort(sec, sec+n,cmp);
	//  The small root heap maintains the maximum value of the right endpoint of all intervals  int  Interval subscript  vector<int>  The right end of the interval   
	priority_queue<int, vector<int>, greater<int>> heap;
	rep(i, 0, n){
		//  Need to open up new areas 
	    if(heap.empty()||heap.top()>=sec[i].l){
	        heap.push(sec[i].r);
	    }else{ //  Update the maximum value of the right endpoint of the current interval 
	        heap.pop();
	        heap.push(sec[i].r);
	    }
	}
	printf("%lld", heap.size());
	return 0;
}

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