线段树练习题

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<algorithm>
 4 #define ls (cur<<1)
 5 #define rs (cur<<1|1)
 6 #define mid ((a[cur].l+a[cur].r)>>1)
 7 #define len(x) (a[x].r-a[x].l+1)
 8 using namespace std;
 9 int n,m,k,x,y;
10 char c;
11 struct tree{int l,r,max;}a[800010];
12 void read(int &k){
13     k=0; int f=1; char c=getchar();
14     while(c<‘0‘||c>‘9‘)c==‘-‘&&(f=-1),c=getchar();
15     while(‘0‘<=c&&c<=‘9‘)k=k*10+c-‘0‘,c=getchar();
16     k*=f;
17 }
18 void pushup(int cur){a[cur].max=max(a[ls].max,a[rs].max);}
19 void build(int cur,int l,int r){
20     a[cur].l=l; a[cur].r=r;
21     if(l<r) build(ls,l,mid),build(rs,mid+1,r),pushup(cur); 
22     else read(a[cur].max);    
23 }
24 void update(int cur,int pos,int x){
25     if(len(cur)==1&&a[cur].l==pos) a[cur].max=max(a[cur].max,x);
26     else update(pos<=mid?ls:rs,pos,x),pushup(cur);
27 }
28 int query(int cur,int l,int r){
29     if(l<=a[cur].l&&a[cur].r<=r) return a[cur].max;
30     int ret=-0X7f7f7f;
31     if(l<=mid) ret=query(ls,l,r);
32     if(r>mid) ret=max(ret,query(rs,l,r));
33     return ret;
34 }
35 int main(){
36     read(n); read(m); build(1,1,n); 
37     for (int i=1;i<=m;i++){
38         while (c!=‘Q‘&&c!=‘U‘) c=getchar();
39         read(x); read(y);
40         if(c==‘Q‘) printf("%d\n",query(1,x,y));
41         else update(1,x,y);
42     }
43     return 0;
44 }