线段树(单点更新) HDU 1754 I Hate It

题目传送门

 1 /*
 2     线段树基本功能：区间最大值，修改某个值
 3 */
 4 #include <cstdio>
 5 #include <cstring>
 6 #include <algorithm>
 7 #define lson l, m, rt << 1
 8 #define rson m+1, r, rt << 1|1
 9
10 const int MAX_N = 200000 + 10;
11 int sum[MAX_N<<2];
12 int a[MAX_N<<2];
13
14 void pushup(int rt)
15 {
16     sum[rt] = sum[rt<<1] + sum[rt<<1|1];
17 }
18
19 void maxrt(int rt)
20 {
21     sum[rt] = std::max (sum[rt<<1], sum[rt<<1|1]);
22 }
23
24 void build(int l, int r, int rt)
25 {
26     if (l == r)
27     {
28         scanf ("%d", &sum[rt]);
29         return ;
30     }
31     int m = (l + r) >> 1;
32     build (lson);
33     build (rson);
34     maxrt (rt);
35 }
36
37 void update(int p, int up, int l, int r, int rt)
38 {
39     if (l == r)
40     {
41         sum[rt] = up;
42         return ;
43     }
44     int m = (l + r) >> 1;
45     if (p <= m)    update (p, up, lson);
46     else    update  (p, up, rson);
47     maxrt (rt);
48 }
49
50 int query(int ql, int qr, int l, int r, int rt)
51 {
52     if (ql <= l && r <= qr)
53     {
54         return sum[rt];
55     }
56     int m = (l + r) >> 1;
57     int ans = 0;
58     if (ql <= m)    ans = std::max(ans, query (ql, qr, lson));
59     if (qr > m)        ans = std::max(ans, query (ql, qr, rson));
60
61     return ans;
62 }
63
64
65 int main(void)        //HDU 1754 I Hate It
66 {
67     //freopen ("inB.txt", "r", stdin);
68     int n, m, ans, b, c;
69     char ch[2];
70
71     while (~scanf ("%d%d", &n, &m))
72     {
73         build (1, n, 1);
74         while (m--)
75         {
76             scanf ("%s%d%d", &ch, &b, &c);
77             if (ch[0] == ‘Q‘)
78             {
79                 ans = query (b, c, 1, n, 1);
80                 printf ("%d\n", ans);
81             }
82             if (ch[0] == ‘U‘)
83             {
84                 update (b, c, 1, n, 1);
85             }
86         }
87     }
88
89     return 0;
90 }