【HDU】5700 - 区间交（线段树 & 贪心）

   5 2 3
1 2 3 4 6
4 5
2 5
1 4

   10

#include <stdio.h>
#include <cstring>
#include <algorithm>
using namespace std;
#define CLR(a,b) memset(a,b,sizeof(a))
#define INF 0x3f3f3f3f
#define LL long long
#define MAX 100000
#define L o<<1
#define R o<<1|1
LL sum[MAX+5];
struct node
{
	int st,endd;
}a[MAX+5];
struct Tree
{
	int l,r;
	int cover;
}tree[MAX<<2];
bool cmp(node a,node b)
{
	return a.st < b.st;
}
void PushUp(int o)
{
	tree[o].cover = tree[L].cover + tree[R].cover;
}
void Build(int o,int l,int r)
{
	tree[o].l = l;
	tree[o].r = r;
	if (l == r)
	{
		tree[o].cover = 0;		//覆盖点全部初始化为0 
		return;
	}
	int mid = (l + r) >> 1;
	Build(L , l , mid);
	Build(R , mid + 1 , r);
	PushUp(o);
}
void UpDate(int o,int x)		//x位置cover值加一 
{
	if (tree[o].l == tree[o].r)
	{
		tree[o].cover++;
		return;
	}
	int mid = (tree[o].l + tree[o].r) >> 1;
	if (mid >= x)
		UpDate(L , x);
	else
		UpDate(R , x);
	PushUp(o);
}
int Query(int o,int x)		//满足条件的最靠右的端点下标 
{
	if (tree[o].l == tree[o].r)
		return tree[o].l;
	if (tree[R].cover >= x)		//优先从右树中找满足条件的
		return Query(R , x);
	else
		return Query(L , x-tree[R].cover);		//右边不够剩下的点从左树找 
}
int main()
{
	int n,k,m;
	int t;
	while (~scanf ("%d %d %d",&n,&k,&m))
	{
		sum[0] = 0;
		for (int i = 1 ; i <= n ; i++)
		{
			scanf ("%d",&t);
			sum[i] = sum[i-1] + t;
		}
		for (int i = 1 ; i <= m ; i++)
			scanf ("%d %d",&a[i].st,&a[i].endd);
		sort (a+1 , a+1+m , cmp);		//对左端点排序 
		Build(1,1,n);
		for (int i = 1 ; i <= k ; i++)		//前k-1个数的左端点不用枚举，直接更新其右端点即可 
			UpDate(1,a[i].endd);
		LL ans = 0;
		a[m+1].endd = 1;		//随便赋值一个，防止最后一次循环出问题 
		for (int i = k ; i <= m ; i++)		//从第k个点开始
		{
			int pos = Query(1,k);
			if (pos >= a[i].st)
				ans = max (ans , sum[pos] - sum[a[i].st-1]);
			UpDate(1,a[i+1].endd);		//将下一点的右端点加入，即其cover值加一 
		}
		printf ("%lld\n",ans);
	}
	return 0;
}