I Hate It 线段树

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <algorithm>
 4 using namespace std;
 5 
 6 int n,m,a[200005],ma[600005],id,ad,ql,qr;
 7 
 8 void build(int o,int l,int r)
 9 {
10     if(l==r){
11         ma[o]=a[l];
12         return;
13     }
14     int mid=(l+r)/2;
15     build(o*2,l,mid);
16     build(o*2+1,mid+1,r);
17     ma[o]=max(ma[o*2],ma[o*2+1]);
18 }
19 
20 void update(int o,int l,int r)
21 {
22     if(l==r){
23         if(l==id){
24             a[l]=ad;
25             ma[o]=ad;
26         }
27         return;
28     }
29     int mid=(l+r)/2;
30     if(id<=mid){
31         update(o*2,l,mid);
32     }
33     else{
34         update(o*2+1,mid+1,r);
35     }
36     ma[o]=max(ma[o*2],ma[o*2+1]);
37 }
38 
39 int quary(int o,int l,int r)
40 {
41     if(ql<=l && qr>=r)
42         return ma[o];
43     int mid=(l+r)/2;
44     int ans1=0,ans2=0;
45     if(ql<=mid){
46         ans1=quary(o*2,l,mid);
47     }
48     if(qr>mid){
49         ans2=quary(o*2+1,mid+1,r);
50     }
51     return max(ans1,ans2);
52 }
53 
54 int main()
55 {
56     int i,j,k,x,y;
57     char str[10];
58     while(scanf("%d %d",&n,&m)!=EOF)
59     {
60         memset(ma,0,sizeof(ma));
61         for(i=1;i<=n;i++)
62             scanf("%d",&a[i]);
63         build(1,1,n);
64         while(m--)
65         {
66             scanf("%s",str);
67             scanf("%d %d",&x,&y);
68             if(str[0]==‘Q‘)
69             {
70                 ql=x,qr=y;
71                 printf("%d\n",quary(1,1,n));
72             }
73             else if(str[0]==‘U‘)
74             {
75                 id=x,ad=y;
76                 update(1,1,n);
77             }
78         }
79     }
80     return 0;
81 }