hdu1574 I Hate It （线段树，查询区间最大值）

 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 #define M 200200
 5 #define inf 0x3f3f3f3f
 6 struct segTree
 7 {
 8     int l,r,elem;
 9     int mid()
10     {
11         return (l+r)/2;
12     }
13 }tree[4*M];
14 int n,m,ans;
15 void buildTree (int now,int left,int right)
16 {
17     tree[now].l=left;
18     tree[now].r=right;
19     if (left==right)
20     {
21         scanf("%d",&tree[now].elem);
22         return;
23     }
24     int middle=tree[now].mid();
25     buildTree(now<<1,left,middle);
26     buildTree(now<<1|1,middle+1,right);
27     tree[now].elem=max(tree[now<<1].elem,tree[now<<1|1].elem);
28 }
29 void update (int now,int left,int right,int x,int change)
30 {
31     if (left==right)
32     {
33         tree[now].elem=change;
34         return;
35     }
36     int middle=tree[now].mid();
37     if (x<=middle)
38     update(now<<1,left,middle,x,change);
39     else
40     update(now<<1|1,middle+1,right,x,change);
41     tree[now].elem=max(tree[now<<1].elem,tree[now<<1|1].elem);
42 }
43 void query (int now,int left,int right,int L,int R)
44 {
45     if (L<=left&&right<=R)
46     {
47         ans=max(ans,tree[now].elem);
48         return ;
49     }
50     int middle=tree[now].mid();
51     if (R<=middle)
52     query(now<<1,left,middle,L,R);
53     else if (L>middle)
54     query(now<<1|1,middle+1,right,L,R);
55     else
56     {
57          query(now<<1,left,middle,L,R);
58          query(now<<1|1,middle+1,right,L,R);
59     }
60 }
61 int main()
62 {
63     //freopen("de.txt","r",stdin);
64     while (~scanf("%d%d",&n,&m))
65     {
66         buildTree(1,1,n);
67         char op[6];
68         while (m--)
69         {
70             int x,y;
71             scanf("%s",op);
72             scanf("%d%d",&x,&y);
73             if (op[0]==‘U‘)
74             update(1,1,n,x,y);
75             else
76             {
77                 ans=-inf;
78                 query(1,1,n,x,y);
79                 printf("%d\n",ans);
80             }
81         }
82     }
83     return 0;
84 }