杭电1754：http://hdu.hustoj.com/showproblem.php?pid=1754
该题为标准的线段树，线段树的基础模型如下：
总共分为三个阶段：
1.建树
建树的时候要考虑到数组的大小
void BuildTree(int i,int left ,int right){ //（当前的数组下标，左范围，右范围） node[i].left = left; node[i].right = right; node[i].value = 0; if (left == right){ father[left] = i; return; } BuildTree(i << 1, left, (int)(floor((left + right) / 2.0))); //建立左子树 BuildTree((i << 1) + 1, (int)(floor((left + right) / 2.0)) + 1, right); //建立右子树 }
2.更新
void Update(int ri){ //更新，从下往上更新 if (ri == 1) return; int fi = ri / 2; int a = node[fi << 1].value; int b = node[(fi << 1) + 1].value; node[fi].value = max(a, b); Update(fi); }
3.区间查询
void Query(int i, int l, int r){ if (node[i].left == l && node[i].right == r){ Max = max(Max, node[i].value); return; } i = i << 1; if (l <= node[i].right){ if (r <= node[i].right) Query(i, l, r); else Query(i, l, node[i].right); } i++; if (r >= node[i].left){ if (l >= node[i].left) Query(i, l, r); else Query(i, node[i].left, r); } }
总代码：
1 #include <iostream> 2 #include <algorithm> 3 #include <string> 4 5 using namespace std; 6 const int MAXNODE = 1 << 19; 7 const int MAXN = 2e5 + 5; 8 9 struct Node{ 10 int value; 11 int right, left; 12 }node[MAXNODE]; 13 14 int father[MAXN]; 15 16 void BuildTree(int i,int left ,int right){ 17 //（当前的数组下标，左范围，右范围） 18 node[i].left = left; 19 node[i].right = right; 20 node[i].value = 0; 21 if (left == right){ 22 father[left] = i; 23 return; 24 } 25 BuildTree(i << 1, left, (int)(floor((left + right) / 2.0))); 26 //建立左子树 27 BuildTree((i << 1) + 1, (int)(floor((left + right) / 2.0)) + 1, right); 28 //建立右子树 29 } 30 31 void Update(int ri){ 32 //更新，从下往上更新 33 if (ri == 1) 34 return; 35 int fi = ri / 2; 36 int a = node[fi << 1].value; 37 int b = node[(fi << 1) + 1].value; 38 node[fi].value = max(a, b); 39 Update(fi); 40 } 41 42 int Max = -1 << 20; 43 void Query(int i, int l, int r){ 44 if (node[i].left == l && node[i].right == r){ 45 Max = max(Max, node[i].value); 46 return; 47 } 48 i = i << 1; 49 if (l <= node[i].right){ 50 if (r <= node[i].right) Query(i, l, r); 51 else Query(i, l, node[i].right); 52 } 53 i++; 54 if (r >= node[i].left){ 55 if (l >= node[i].left) Query(i, l, r); 56 else Query(i, node[i].left, r); 57 } 58 59 } 60 61 int main(){ 62 int n, m; 63 ios::sync_with_stdio(false); 64 while (cin >> n >> m){ 65 BuildTree(1, 1, n); 66 for (int i = 1; i <= n; i++){ 67 int x; 68 cin >> x; 69 node[father[i]].value = x; 70 Update(father[i]); 71 } 72 string s; 73 while (m--){ 74 int x, y; 75 cin >> s; 76 cin >> x >> y; 77 if (s == "Q"){ 78 Max = 0; 79 Query(1, x, y); 80 cout << Max << endl; 81 } 82 else if (s == "U"){ 83 node[father[x]].value = y; 84 Update(father[x]); 85 } 86 } 87 } 88 // system("pause"); 89 return 0; 90 }