HDU 1754线段树基本操作，建树，更新，查询

代码线段树入门整理中有介绍、

 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<cmath>
 using namespace std;
 const int MAXNODE=<<;
 const int MAX=;
 struct NODE{
     int left,right;
     int value;
 }node[MAXNODE];
 int father[MAX];
 void buildtree(int i,int left,int right)
 {
     node[i].left=left;
     node[i].right=right;
     node[i].value=;
     if(left==right){
         father[left]=i;
         return;
     }
     buildtree(i<<, left, (int)floor( (right+left) / 2.0));
     buildtree((i<<) + , (int)floor( (right+left) / 2.0) + , right);  

 }
 void updatatree(int ri)
 {
     if(ri==)    return;
     int fi=ri/;
     int a=node[fi<<].value;
     int b=node[(fi<<)+].value;
     node[fi].value=a>b?a:b;
     updatatree(ri/);
 }
 int maxn;
 void query(int i,int l,int r)
 {
     if(node[i].left==l&&node[i].right==r){
         maxn=(maxn<node[i].value)?node[i].value:maxn;
         return;
     }
     i=i<<;
     if(l<=node[i].right)
         if(r<=node[i].right)
             query(i,l,r);
         else
             query(i,l,node[i].right);
     i+=;
     if(r>=node[i].left)
         if(l>=node[i].left)
             query(i,l,r);
         else
             query(i,node[i].left,r);
 }
 int main()
 {
     int n,m;
     while(~scanf("%d %d",&n,&m)){
         buildtree(,,n);
         int grade;
         for(int i=;i<=n;++i){
             scanf("%d",&grade);
             node[father[i]].value=grade;
             updatatree(father[i]);
         }
         while(m--){
             int x,y;char str[];
             scanf("%s %d %d",str,&x,&y);
             if(str[]=='U'){
                 node[father[x]].value=y;
                 updatatree(father[x]);
             }
             else{
                 maxn=;
                 query(,x,y);
                 printf("%d\n",maxn);
             }
         }
     }
 }