题目意思很简单，很裸的线段树。

有是一道单点更新问题，是单点更新+区间最大值。

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
using namespace std;

#define L(x) (x<<1)
#define R(x) (x<<1|1)
#define lson lft,mid,rt << 1
#define rson mid+1,rht,rt << 1 | 1
#define MID(a,b) (a+((b-a)>>1))
#define INF 1<<30

const int MAXN = 200005;
struct Node{
   int lft,rht,mx;
   int mid(){return MID(lft,rht);}
};
Node tree[4*MAXN];
int y[MAXN],n,m;
class Segtree{
public:
    void Build(int lft,int rht,int rt){
        tree[rt].lft = lft; tree[rt].rht = rht;
        tree[rt].mx = -INF;
        if(lft == rht)
           tree[rt].mx = y[lft];
        else{
            int mid = tree[rt].mid();
            Build(lson);
            Build(rson);
            tree[rt].mx = max(tree[L(rt)].mx,tree[R(rt)].mx);
        }
    }
    void Update(int pos,int rt,int val){
        int lft = tree[rt].lft,rht = tree[rt].rht;
        if(lft == rht){
            tree[rt].mx = val;
        }
        else{
            int mid = tree[rt].mid();
            if(pos <= mid) Update(pos,L(rt),val);
            else Update(pos,R(rt),val);
            tree[rt].mx = max(tree[L(rt)].mx,tree[R(rt)].mx);
        }
   }
   int Query(int st,int ed,int rt){
       int lft = tree[rt].lft,rht = tree[rt].rht;
       if(st <= lft&&rht <= ed) return tree[rt].mx;
       else{
            int mid = tree[rt].mid();
            int mx1 = -INF,mx2 = -INF;
            if(st <= mid) mx1 = Query(st,ed,L(rt));
            if(ed > mid) mx2 = Query(st,ed,R(rt));
            return max(mx1,mx2);
       }
   }
};

int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        Segtree seg;
        char op[5];
        int a,b;
        for(int i = 1;i <= n;++i)
            scanf("%d",&y[i]);
        seg.Build(1,n,1);
        while(m--){
            scanf("%s%d%d",op,&a,&b);
            if(op[0] == 'Q')
               printf("%d\n",seg.Query(a,b,1));
            else
               seg.Update(a,1,b);
        }
    }
    return 0;
}