[HDU1754]I Hate It线段树裸题

http://acm.hdu.edu.cn/showproblem.php?pid=1754

解题关键：刚开始死活超时，最后发现竟然是ch，和t1、t2每次循环都定义的锅，以后养成建全局变量的习惯。

注意背模板时，find时最后无赋值

 #include<bits/stdc++.h>
 using namespace std;
 typedef long long ll;
 struct node{
     int left,right,max;
 }tree[];
 int num[];
 char ch;
 int t1,t2;
 int build(int root,int left,int right){
     tree[root].left=left;
     tree[root].right=right;
     if(left==right) return tree[root].max=num[left];

     int a,b,mid;
     mid=(left+right)/;
     a=build(*root,left,mid);
     b=build(*root+,mid+,right);
     return tree[root].max=max(a,b);
 }

 int find(int root,int left,int right){
     if(right<tree[root].left||left>tree[root].right) return ;
     if(left<=tree[root].left&&tree[root].right<=right) return tree[root].max;

     int a,b;
     a=find(*root,left,right);
     b=find(*root+,left,right);
     return max(a,b);//find时不能赋值
 }

 int update(int root,int pos,int val){
     if(pos<tree[root].left||pos>tree[root].right) return tree[root].max;
     if(pos==tree[root].left&&pos==tree[root].right) return tree[root].max=val;

     int a,b;
     a=update(*root,pos,val);
     b=update(*root+,pos,val);
     return tree[root].max=max(a,b);
 }
 int n,m;
 int main(){
     while(scanf("%d%d",&n,&m)!=EOF){
         memset(num,,sizeof num);
         memset(tree,,sizeof tree);
         for(int i=;i<=n;i++){
             scanf("%d",num+i);
         }
         build(,,n);
         for(int i=;i<m;i++){
             getchar();
             scanf("%c%d%d",&ch,&t1,&t2);
             if(ch=='Q'){
                 int res=find(,t1,t2);
                 printf("%d\n",res);
             }
             else{
                 update(,t1,t2);
             }
         }
     }

 }