POJ 3264 线段树

参考：http://blog.youkuaiyun.com/metalseed/article/details/8039326    线段树的讲解

 

#include<iostream>   
using namespace std;   
#define MAXN 50005       

int min(int x,int y)
{
    return x<y?x:y;    
} 
int max(int x,int y)
{
    return x>y?x:y;    
} 
struct STreeNode
{   
     int left ,right;//left 结点的左端点 
     int maxv,minv;  // 结点的值 
};
STreeNode  STree[MAXN*4]; //线段树节点个数
int a[MAXN],ansmax,ansmin; 
//建立线段树
void build(int L ,int R ,int id)
{  
     //left,right分别为当前节点的左右端点,id为节点在数组中的编号    
    STree[id].left=L;   
    STree[id].right=R;      
    int mid=(L+R)/2; 
    if(L==R)
      {
        STree[id].maxv=STree[id].minv=a[L];
        return;             
      }       
    //递归的建立左右子树         
    build(L,mid,id*2);        
    build(mid+1,R,id*2+1);    
    STree[id].maxv=max(STree[id*2].maxv,STree[id*2+1].maxv);
    STree[id].minv=min(STree[id*2].minv,STree[id*2+1].minv); 
} 
void query(int left,int right,int id)
{
     //当前结点完全包含于查询区间 [left,right] 
    if(left<=STree[id].left&&right>=STree[id].right) 
    {
        ansmax=max(STree[id].maxv,ansmax);
        ansmin=min(STree[id].minv,ansmin);
        return;
    }
    int mid=(STree[id].left+STree[id].right)/2;
    if(mid<left)
      query(left,right,id*2+1);//只进入右子树 
    else if(mid>=right) query(left,right,id*2);//只左子树 
    else 
    {
        query(left,right,id*2); 
        query(left,right,id*2+1);
    }
} 
int main()   
{      
    int n,q,i,x,y;
    while(scanf("%d%d",&n,&q)!=EOF)
    {
     for(i=1;i<=n;i++)
       scanf("%d",&a[i]);
     build(1,n,1); 
     for(i=0;i<q;i++)
     {
        scanf("%d%d",&x,&y);
        ansmax=-1;  //注意初始化 
        ansmin=INT_MAX;
        query(x,y,1); 
       // printf("%d  %d\n",ansmax,ansmin); 
        printf("%d\n",ansmax-ansmin);              
     }                               
    } 
   // system("pause");
    return 0;   
}