hdoj1754 线段树单点更新

题目中文的，不解释了
维护一个最大值的线段树
 1 #include <stdio.h>
 2 
 3 #define lson l, m, rt<<1
 4 #define rson m+1, r, rt<<1|1
 5 
 6 const int maxn = 200000;
 7 
 8 char cmd[2];
 9 int  n, mNum, a, b, max[maxn<<2];
10 
11 int Max(int x, int y)
12 {
13     return (x>y ? x:y);
14 }/* Max */
15 
16 void BuildTree(int l, int r, int rt)
17 {
18     if (l == r)
19     {
20         scanf("%d", &max[rt]);
21         return ;
22     }/* End of If */
23     
24     int m = (l+r)>>1;
25     BuildTree(lson);
26     BuildTree(rson);
27     max[rt] = Max(max[rt<<1], max[rt<<1|1]);    /* Push Up */
28 }/* BuildTree */
29 
30 int Query(int L, int R, int l, int r, int rt)
31 {
32     if (L<=l && r<=R)
33         return max[rt];
34     
35     int ret=-1, m=(l+r)>>1;
36 
37     if (L <= m)
38         ret = Max(ret, Query(L, R, lson));
39     if (R > m)
40         ret = Max(ret, Query(L, R, rson));
41 
42     return ret;
43 }/* Query */
44 
45 void UpData(int p, int bi, int l, int r, int rt)
46 {
47     if (l == r)
48     {
49         max[rt] = bi;
50         return ;
51     }/* End of If */
52 
53     int m = (l+r)>>1;
54 
55     if (p <= m)
56         UpData(p, bi, lson);
57     else
58         UpData(p, bi, rson);
59         
60     max[rt] = Max(max[rt<<1], max[rt<<1|1]);    /* Push Up */
61 }/* UpData */
62 
63 int main()
64 {
65     while (~scanf("%d %d", &n, &mNum))
66     {
67         BuildTree(1, n, 1);
68         for (int i=1; i<=mNum; ++i)
69         {
70             scanf("%s %d %d", cmd, &a, &b);
71             if (cmd[0] == 'Q')  /* Query */
72                 printf("%d\n", Query(a, b, 1, n, 1));
73             else    /* UpData */
74                 UpData(a, b, 1, n, 1);
75         }
76     }/* End of While */
77     
78     return 0;
79 }