HDU 1754 - I Hate It 题解

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cmath>
 4 #include<cstring>
 5 
 6 using namespace std;
 7 const int MAXN = 500005;
 8 
 9 inline void read(int &x)
10 {
11     char ch = getchar(),c = ch;x = 0;
12     while(ch < ‘0‘ || ch > ‘9‘) c = ch,ch = getchar();
13     while(ch >= ‘0‘ && ch <= ‘9‘) x = (x<<1)+(x<<3)+ch-‘0‘,ch = getchar();
14     if(c == ‘-‘) x = -x;
15 }
16 
17 int sdata[MAXN<<1],num[MAXN],n,m,a,b;
18 char op[5];
19 
20 inline int max(int a,int b)
21 {
22     return a>b?a:b;
23 }
24 
25 inline void update(int o)
26 {
27     sdata[o] = max(sdata[o<<1],sdata[o<<1|1]);
28 }
29 
30 void build(int l,int r,int o)
31 {
32     if(l == r)
33     {
34         read(sdata[o]);
35         return;
36     }
37     int mid = (l+r)>>1;
38     build(l,mid,o<<1);
39     build(mid+1,r,o<<1|1);
40     update(o);
41 }
42 
43 void modify(int l,int r,int o,int p,int k)
44 {
45     if(l == r && r == p)
46     {
47         sdata[o] = k;
48         return;
49     }
50     int mid = (l+r)>>1;
51     if(p <= mid) modify(l,mid,o<<1,p,k);
52     else modify(mid+1,r,o<<1|1,p,k);
53     update(o);
54 }
55 
56 int ask(int l,int r,int o,int ll,int rr)
57 {
58     if(ll <= l && rr >= r)
59     {
60         return sdata[o];
61     }
62     int mid = (l+r)>>1;
63     int ans = 0;
64     if(ll <= mid) ans = max(ans,ask(l,mid,o<<1,ll,rr));
65     if(rr > mid) ans = max(ans,ask(mid+1,r,o<<1|1,ll,rr));
66     return ans;
67 }
68 
69 int main()
70 {
71     while(scanf("%d%d",&n,&m) != EOF)
72     {
73         memset(sdata,0,sizeof(sdata));
74         build(1,n,1);
75         for(int i = 1;i <= m;++ i)
76         {
77             scanf("%s",op);
78             read(a),read(b);
79             if(op[0] == ‘Q‘)
80             {
81                 printf("%d\n",ask(1,n,1,a,b));
82             }
83             else
84             {
85                 modify(1,n,1,a,b);
86             }
87         }    
88     }
89     return 0;
90 }