I Hate It HDU - 1754 (线段树)

 1 #include<iostream>
 2 #include<vector>
 3 #include<string>
 4 #include<cmath>
 5 #include<set>
 6 #include<algorithm>
 7 #include<cstdio>
 8 #include<map>
 9 #include<cstring>
10 #include<list>
11 
12 #define MAXSIZE 200010
13 
14 using namespace std;
15 
16 int N, M;
17 int tree[4*MAXSIZE];
18 int ans = -1;
19 
20 void init()
21 {
22     memset(tree, 0, sizeof(tree));
23 }
24 
25 
26 void build(int node, int l, int r)
27 {
28     if(l == r)
29     {
30         scanf("%d", &tree[node]);
31         return;
32     }
33     int mid = (l+r)/2;
34     build(node*2, l, mid);
35     build(node*2+1, mid+1, r);
36     
37     tree[node] = max(tree[node*2], tree[node*2+1]);
38 }
39 
40 // 单点更新 
41 void update(int node, int l, int r, int index, int n)
42 {
43     if(l == r)
44     {
45         tree[node] = n;
46         return;
47     }
48     int mid = (l+r)/2;
49     if(index <= mid)
50         update(node*2, l, mid, index, n);
51     else
52         update(node*2+1, mid+1, r, index, n);
53         
54     tree[node] = max(tree[node*2], tree[node*2+1]);
55 }
56 
57 
58 // 区间查询 
59 int query_range(int node, int l, int r, int L, int R)
60 {
61     if(l <= L && r >= R)
62         return tree[node];
63     int mid = (L+R)/2;
64     if(l <= mid)
65         ans = max(ans, query_range(node*2, l, r, L, mid));
66     if(mid < r)
67         ans = max(ans, query_range(node*2+1, l, r, mid+1, R));
68     
69     return ans;
70 }
71 
72 int main()
73 {    
74     while(scanf("%d%d", &N, &M) != EOF)
75     {
76         init();
77         build(1,1,N);
78         for(int j = 0; j < M; ++j)
79         {
80             char c;
81             int a, b;
82             scanf(" %c%d%d", &c, &a, &b);    // scanf中%c会读取空格和回车，所以在%c前面加一个空格 
83             if(c == ‘Q‘)
84             {
85                 printf("%d\n", query_range(1, a, b, 1, N));
86                 ans = -1;
87             }
88             else if(c == ‘U‘)
89                 update(1, 1, N, a, b); 
90         }
91     }
92 
93     return 0;
94 }