线段树解决区间覆盖问题

问题：

/*************************************************************************
* File Name: Solution.cpp
* Description:
* Author: Yuji CAO
* Mail: caoyuji@sogou-inc.com
* Created_Time: 2015-08-03 10时44分46秒
* Last modified: 2015-08-03 10时44分46秒
************************************************************************/
#include<iostream>
#include<vector>
#include<string>
#include<map>
#include<set>
#include<limits>
using namespace std;

struct TTNode{
int _val;
int _start;
int _end;
TTNode* _left;
TTNode* _right;
TTNode(int s,int e,int v):_val(v),_start(s),_end(e),_left(NULL),_right(NULL){}
TTNode(const TTNode& ttn){
this->_val=ttn._val;
this->_start=ttn._start;
this->_end=ttn._end;
this->_left=ttn._left;
this->_right=ttn._right;
}
TTNode& operator=(const TTNode& ttn){
this->_val=ttn._val;
this->_start=ttn._start;
this->_end=ttn._end;
this->_left=ttn._left;
this->_right=ttn._right;
return *this;
}
static void visit(TTNode* root){
if(root==NULL){return;}
cout<<"["<<root->_start<<","<<root->_end<<";"<<root->_val<<"]"<<endl;
visit(root->_left);
visit(root->_right);
}
};

class TreadTree{
public:
void build(TTNode* &cur,int l,int r){
if(r==l+1){
cur=new TTNode(l,r,0);
return;
}else{
cur=new TTNode(l,r,0);
build(cur->_left,l,(l+r)/2);
build(cur->_right,(l+r)/2,r);
}
}
void insert(TTNode* &root,int l,int r){
if(l==r){
return ;
}
if(root->_val==0){
if(root->_start>=l&&root->_end<=r){
root->_val=1;
return ;
}else{
int mid=(root->_start+root->_end)/2;
if(l<mid){
int e=min(mid,r);
insert(root->_left,l,e);
}
if(r>=mid){
int s=max(mid,l);
insert(root->_right,s,r);
}
}
}
}
int query(TTNode* root){
if(root==NULL){
return 0;
}
if(root->_val==1){
int ret=root->_end-root->_start;
return ret;
}else{
int ret=0;
ret+=query(root->_left);
ret+=query(root->_right);
return ret;
}
}
void query(vector<TTNode>& result,TTNode* root,int start,int end){
if(root->_start>start||root->_end<end){
return;
}
if(root->_start==start&&root->_end==end){
result.push_back(*root);
return ;
}
int mid=(root->_start+root->_end)/2;
if(start<=mid){
int e=min(mid,end);
query(result,root->_left,start,e);
}
if(end>mid){
int e=min(end,root->_end);
query(result,root->_right,mid,e);
}
}
};
struct Segment{
int _start;
int _end;
Segment(int s,int e):_start(s),_end(e){}
};
/*
*get result
*/
int getResult(vector<Segment>& dat){
int b=numeric_limits<int>::max();
int e=numeric_limits<int>::min();
for(auto ele:dat){
if(ele._start<b){
b=ele._start;
}
if(ele._end>e){
e=ele._end;
}
}

TreadTree tt;
TTNode* root=NULL;
tt.build(root,b,e);
for(auto ele:dat){
tt.insert(root,ele._start,ele._end);
}
return tt.query(root);
}

int main(){
int m;
cin>>m;
vector<Segment> dat;
for(int i=0;i<m;++i){
Segment sm(0,0);
cin>>sm._start>>sm._end;
dat.push_back(sm);
}
cout<<getResult(dat)<<endl;
}