线段树(单点更新) HDU 1754 I Hate It

题目传送门

 /*
     线段树基本功能：区间最大值，修改某个值
 */
 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #define lson l, m, rt << 1
 #define rson m+1, r, rt << 1|1

 const int MAX_N =  + ;
 int sum[MAX_N<<];
 int a[MAX_N<<];

 void pushup(int rt)
 {
     sum[rt] = sum[rt<<] + sum[rt<<|];
 }

 void maxrt(int rt)
 {
     sum[rt] = std::max (sum[rt<<], sum[rt<<|]);
 }

 void build(int l, int r, int rt)
 {
     if (l == r)
     {
         scanf ("%d", &sum[rt]);
         return ;
     }
     int m = (l + r) >> ;
     build (lson);
     build (rson);
     maxrt (rt);
 }

 void update(int p, int up, int l, int r, int rt)
 {
     if (l == r)
     {
         sum[rt] = up;
         return ;
     }
     int m = (l + r) >> ;
     if (p <= m)    update (p, up, lson);
     else    update  (p, up, rson);
     maxrt (rt);
 }

 int query(int ql, int qr, int l, int r, int rt)
 {
     if (ql <= l && r <= qr)
     {
         return sum[rt];
     }
     int m = (l + r) >> ;
     int ans = ;
     if (ql <= m)    ans = std::max(ans, query (ql, qr, lson));
     if (qr > m)        ans = std::max(ans, query (ql, qr, rson));

     return ans;
 }

 int main(void)        //HDU 1754 I Hate It
 {
     //freopen ("inB.txt", "r", stdin);
     int n, m, ans, b, c;
     char ch[];

     while (~scanf ("%d%d", &n, &m))
     {
         build (, n, );
         while (m--)
         {
             scanf ("%s%d%d", &ch, &b, &c);
             if (ch[] == 'Q')
             {
                 ans = query (b, c, , n, );
                 printf ("%d\n", ans);
             }
             if (ch[] == 'U')
             {
                 update (b, c, , n, );
             }
         }
     }

     return ;
 }