HDU1754线段树

#include<iostream>
#include<cstdio>
using namespace std;
struct node{
int s;
int l,r;
};
struct node tree[2000100];
int a[200010];
int create_tree(int h,int x,int y){//建树
int mid=(x+y)/2;//中间
tree[h].l=x;tree[h].r=y;
if(x==y){//如果左右范围相等
tree[h].s=a[x];
return tree[h].s;
}
int a=create_tree(2*h,x,mid);//向两边分开递归
int b=create_tree(2*h+1,mid+1,y);
tree[h].s=a>b?a:b;
return tree[h].s;
}
int Q(int h,int x,int y){//询问
if(y<tree[h].l || x>tree[h].r)//如果需要查询的范围不在原来的范围内
return 0;
if(x<=tree[h].l && y>=tree[h].r)//如果需要查询的范围刚好匹配
return tree[h].s;
int a=Q(2*h,x,y);//向两侧分别递归
int b=Q(2*h+1,x,y);
return a>b?a:b;;
}
int U(int h,int x){//更新
if(x<tree[h].l || x>tree[h].r)
return tree[h].s;
if(tree[h].l==tree[h].r){
tree[h].s=a[tree[h].l];
return tree[h].s;
}
int a=U(2*h,x);
int b=U(2*h+1,x);
tree[h].s=a>b?a:b;
return tree[h].s;
}
int main(){
int i,j,k,m,n,x,y;
while(scanf("%d%d",&n,&m)!=EOF){
for(i=1;i<=n;i++)scanf("%d",&a[i]);
create_tree(1,1,n);
for(i=1;i<=m;i++){
char c;
getchar();
scanf("%c%d%d",&c,&x,&y);
if(c=='Q'){
cout<<Q(1,x,y)<<endl;
}else{
a[x]=y;
U(1,x);
}
}
}
return 0;
}