HDU 1754 I Hate It（线段树基础应用）

　　基础线段树

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
#define maxn 200010
#define lson p<<1
#define rson p<<1|1
struct NOD
{
    int l,r;
    int best;
} node[maxn<<4];
void build(int l,int r,int p)
{
    node[p].l = l,node[p].r = r;
    if(l == r)
    {
        scanf("%d",&node[p].best);
        return;
    }
    int mid = (l+r) >> 1;
    build(l,mid,lson);
    build(mid+1,r,rson);
    node[p].best = max(node[lson].best,node[rson].best);
}
int ask(int l,int r,int p)
{
    if(node[p].l == l && node[p].r == r)
    {
        return node[p].best;
    }
    int mid = (node[p].l+node[p].r)>>1;
    if(r <= mid)
        return ask(l,r,lson);
    else if(l >= mid+1)
        return ask(l,r,rson);
    else return max(ask(l,mid,lson),ask(mid+1,r,rson));
}
void updata(int id,int num,int p)
{
    if(node[p].l==node[p].r && node[p].l == id)
    {
        node[p].best = num;
        return;
    }
    int mid = (node[p].l+node[p].r) >> 1;
    if(id <= mid)
    updata(id,num,lson);
    else if(id > mid) updata(id,num,rson);
    node[p].best = max(node[lson].best,node[rson].best);
}
int main()
{
    int n,m;
    while(EOF!=scanf("%d%d",&n,&m))
    {
        build(1,n,1);
        while(m--)
        {
            char op[2];
            scanf("%s",op);
            if(op[0] == 'Q')
            {
                int l,r;
                scanf("%d%d",&l,&r);
                printf("%d\n",ask(l,r,1));
            }
            else
            {
                int id,num;
                scanf("%d%d",&id,&num);
                updata(id,num,1);
            }
        }
    }
    return 0;
}