hdu 1754（线段树）

简单线段树

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;
const int maxn=200000+100;
struct settree
{
    int val;
}tree[maxn*3];
int aa[maxn];
int n,m;
void build(int root,int aa[],int l,int r)
{
    if(l==r)
        tree[root].val=aa[l];
   else
   {
        int mid=(l+r)/2;
      build(root*2,aa,l,mid);
     build(root*2+1,aa,mid+1,r);
     tree[root].val=max(tree[root*2].val,tree[root*2+1].val);
   }
}
void upone(int root,int l,int r,int v,int vval)
{
    if(l==r)
    {
        if(l==v)
            tree[root].val=vval;
        return;
    }
   int mid=(l+r)/2;
   if(v<=mid)
    upone(root*2,l,mid,v,vval);
    else upone(root*2+1,mid+1,r,v,vval);
   tree[root].val=max(tree[root*2].val,tree[root*2+1].val);
}
int serch(int root,int l,int r,int a,int b)
{
    if(b<l||a>r) return 0;
    if(a<=l&&r<=b) return tree[root].val;
    int mid=(l+r)/2;
    int mm=max(serch(root*2,l,mid,a,b),serch(root*2+1,mid+1,r,a,b));
    return mm;
}
int main()
{
   while(~scanf("%d%d",&n,&m))
   {
       for(int i=1;i<=n;i++)
         scanf("%d",&aa[i]);
    build(1,aa,1,n);
       char cc;
       int a,b;
       getchar();
    for(int i=0;i<m;i++)
    {
        scanf("%c %d %d",&cc,&a,&b);
          getchar();
         if(cc=='Q')
         {
             int mm=serch(1,1,n,a,b);
             printf("%d\n",mm);
         }
         else if(cc=='U')
         {
            upone(1,1,n,a,b);
         }
    }
   }
    return 0;
}