线段树（自敲：建树，查找最大值，更新结点值）

HDU1754

 

  1 #include <bits/stdc++.h>

  2 

  3 using namespace std;

  4 

  5 const int MaxSIZE = 2e6 + 10;

  6 

  7 typedef struct {

  8     int Max ;

  9     int left, right ;

 10 } NODE ;

 11 

 12 int     n, m ;

 13 int     num [MaxSIZE] ;

 14 NODE    tree[MaxSIZE * 20] ;

 15 

 16 

 17 int build (int root, int left, int right) {

 18     int mid ;

 19 

 20     tree[root].left     = left ;

 21     tree[root].right    = right ;

 22 

 23     if (left == right) {

 24         return tree[root].Max = num[left] ;

 25     }

 26     mid = (left + right) / 2 ;

 27 

 28 

 29     int a, b ;

 30     a = build (2 * root, left, mid) ;

 31     b = build (2 * root + 1, mid + 1, right) ;

 32 

 33     return tree[root].Max = max (a, b) ;

 34 }

 35 

 36 int Find (int root, int left, int right) {

 37     int mid ;

 38 

 39     if (tree[root].left > right || tree[root].right < left)

 40         return 0 ;

 41 

 42     if (left <= tree[root].left && tree[root].right <= right)

 43         return tree[root].Max ;

 44 

 45     int a, b ;

 46     a = Find (2 * root, left, right) ;

 47     b = Find (2 * root + 1, left, right) ;

 48 

 49     return max (a, b) ;

 50 }

 51 

 52 

 53 int update (int root, int pos, int val) {

 54 

 55     if (pos < tree[root].left || tree[root].right < pos)

 56         return tree[root].Max ;

 57 

 58     if (tree[root].left == pos && tree[root].right == pos)

 59         return tree[root].Max = val ;

 60 

 61     int a, b ;

 62     a = update (2 * root, pos, val) ;

 63     b = update (2 * root + 1, pos, val) ;

 64 

 65     tree[root].Max = max (a, b) ;

 66 

 67     return tree[root].Max ;

 68 }

 69 

 70 

 71 int main() {

 72     int n, ask_n;

 73     while (~scanf("%d%d", &n, &ask_n)) {

 74     //while (cin >> n >> ask_n) {

 75         memset(num, 0, sizeof(num));

 76 

 77         for (int i = 1; i <= n; ++ i) {

 78             //cin >> num[i];

 79             scanf("%d", &num[i]);

 80         }

 81 

 82         build (1, 1, n);

 83 

 84         char op; int x, y;

 85 

 86         for (int j = 0; j < ask_n; ++ j) {

 87             getchar();

 88             scanf("%c%d%d", &op, &x, &y);

 89             //cin >> op >> x >> y;

 90             if (op == 'Q') {

 91                 int ans = Find (1, x, y);

 92                 cout << ans << endl;

 93             } else if (op == 'U') {

 94                 num[x] = y;

 95                 update (1, x, y);

 96             }

 97         }

 98     }

 99     return 0;

100 }