HDU ACM 1698 Just a Hook->线段树+区间修改

分析：线段树的应用，区间修改，使用延迟标记进行延迟修改。

#include<iostream>
using namespace std;

#define N 100010

class SegmentTree
{
private:
	struct Node
	{
		int left,right;     //左右子节点
		int sum;            //区间和
		int lazy;           //延迟标记
	};

public:
	void BuildTree(int root,int l,int r);
	void Change(int root,int l,int r,int c);
	int Query(int root);

private:
	Node m_Tree[N<<2];
};

int SegmentTree::Query(int root)
{
	return m_Tree[root].sum;
}

void SegmentTree::Change(int root,int l,int r,int c)
{
	int mid,x,y;

	x=m_Tree[root].left;
	y=m_Tree[root].right;

	if(l==x && r==y)
	{
		m_Tree[root].lazy=1;
		m_Tree[root].sum=(y-x+1)*c;   //区间的每个点都被修改为c，和就等于点数乘以c
		return ;
	}
	mid=(x+y)>>1;
	if(m_Tree[root].lazy==1)    //该if处理延迟更新
	{
		m_Tree[root].lazy=0;
		Change(2*root+1,x,mid,m_Tree[root].sum/(y-x+1));  //m_Tree[root].sum/(r-l+1)即可得到之前保留的单个点的值
		Change(2*root+2,mid+1,y,m_Tree[root].sum/(y-x+1));
	}
	if(l<=mid) Change(2*root+1,l,mid<r?mid:r,c);    //该两句更新包含三种情况,更新区间在mid左边，在右边，左右两边均有
	if(r>mid) Change(2*root+2,mid+1>l?mid+1:l,r,c);

	m_Tree[root].sum=m_Tree[root*2+1].sum+m_Tree[root*2+2].sum;
}

void SegmentTree::BuildTree(int root,int l,int r)
{
	int mid;

	m_Tree[root].left=l;
	m_Tree[root].right=r;
	m_Tree[root].sum=r-l+1;     //刚开始区间和等于区间的点数
	m_Tree[root].lazy=1;        //设置延迟标记

	if(l==r) return ;
	mid=(l+r)>>1;
	BuildTree(2*root+1,l,mid);     //构建左子树
	BuildTree(2*root+2,mid+1,r);   //构建右子树
}

SegmentTree seg_tree;
int main()
{
	int T,n,Q,X,Y,Z,i;

	scanf("%d",&T);
	i=0;
	while(T--)
	{
		scanf("%d",&n);
		seg_tree.BuildTree(0,0,n-1);
		scanf("%d",&Q);
		while(Q--)
		{
			scanf("%d %d %d",&X,&Y,&Z);
			seg_tree.Change(0,X-1,Y-1,Z);
		}
		printf("Case %d: The total value of the hook is %d.\n",++i,seg_tree.Query(0));
	}
	return 0;
}