线段树---HDU1754 I hate it

这个题也是线段树的基础题，有了上一个题的基础，在做这个题就显得比较轻松了，大体都是一样的，那个是求和，这个改成求最大值，基本上思路差不多，下面是代码的实现

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4
 5 using namespace std;
 6
 7 const int MAX = 200010 * 4;
 8 int segment[MAX];
 9 //向上调整
10 void pushUp(int root)
11 {
12     segment[root] = max(segment[root * 2], segment[root * 2 + 1]);
13 }
14
15 void buildTree(int root, int left, int right)
16 {
17     if(left == right)
18     {
19         scanf("%d", &segment[root]);
20         return;
21     }
22     int mid = (left + right) / 2;
23     buildTree(root * 2, left, mid);
24     buildTree(root * 2 + 1, mid + 1, right);
25     //要把跟他上面所有关联的节点都要更新
26     pushUp(root);
27 }
28 //更新节点
29 void update(int root, int pos, int update_num, int left, int right)
30 {
31     if(left == right)
32     {
33         segment[root] = update_num;
34         return;
35     }
36     int mid = (left + right) / 2;
37     if(pos <= mid)
38     {
39         update(root * 2, pos, update_num, left, mid);
40     }
41     else
42     {
43         update(root * 2 + 1, pos, update_num, mid + 1, right);
44     }
45     pushUp(root);
46 }
47 //left和right为要查找的区间，L和R为当前查到了哪个区间
48 int getMax(int root, int left, int right, int L, int R)
49 {
50     if(L == left && R == right)
51     {
52         return segment[root];
53     }
54     int mid = (left + right) / 2;
55     int Max_Num = 0;
56     if(R <= mid)
57     {
58         Max_Num = getMax(root * 2, left, mid, L, R);
59     }
60     else if(L > mid)
61     {
62         Max_Num = getMax(root * 2 + 1, mid + 1, right, L, R);
63     }
64     else
65     {
66         Max_Num = getMax(root * 2, left, mid, L, mid);
67         Max_Num = max(Max_Num, getMax(root * 2 + 1, mid + 1, right, mid + 1, R));
68     }
69     return Max_Num;
70 }
71
72 int main()
73 {
74     int N, M;
75     while(~scanf("%d %d", &N, &M))
76     {
77         memset(segment, 0, sizeof(segment));
78         buildTree(1, 1, N);
79         char ch;
80         int t1, t2;
81         for(int i = 0; i < M; i++)
82         {
83             getchar();
84             scanf("%c %d %d", &ch, &t1, &t2);
85             if(ch == ‘U‘)
86             {
87                 update(1, t1, t2, 1, N);
88             }
89             else
90             {
91                 printf("%d\n", getMax(1, 1, N, t1, t2));
92             }
93         }
94     }
95     return 0;
96 }