思路：

线段树的基本操作：单点替换，区间最值

#include 
    
     #include 
     
      #include 
      
       #include 
       
        using namespace std;#define lhs l, m, rt << 1#define rhs m + 1, r, rt << 1 | 1const int maxn = 200010;int seg[maxn << 2];void pushUp(int rt){
         seg[rt] = max(seg[rt << 1], seg[rt << 1 | 1]);}void build(int l, int r, int rt){
         if (l == r)    {
             scanf("%d", &seg[rt]);        return;    }    int m = (l + r) >> 1;    build(lhs);    build(rhs);    pushUp(rt);}void update(int p, int delta, int l, int r, int rt){
         if (l == r)    {
             seg[rt] = delta;        return;    }    int m = (l + r) >> 1;    if (p <= m)        update(p, delta, lhs);    else        update(p, delta, rhs);    pushUp(rt);}int query(int beg, int end, int l, int r, int rt){
         if (beg <= l && r <= end)        return seg[rt];    int m = (l + r) >> 1;    int ret = 0;    if (beg <= m)        ret = query(beg, end, lhs);    if (end > m)        ret = max(ret, query(beg, end, rhs));    return ret;}int main(){
         int n, m;    while (scanf("%d %d", &n, &m) != EOF)    {
             build(1, n, 1);        while (m--)        {
                 char op[16];            int a, b;            scanf("%s", op);            scanf("%d %d", &a, &b);            if (op[0] == 'Q')                printf("%d\n", query(a, b, 1, n, 1));            else if (op[0] == 'U')                update(a, b, 1, n, 1);        }    }    return 0;}