hdoj1754 线段树--单点更新

题目中文的，不解释了

维护一个最大值的线段树

 1 #include <stdio.h>

 2 

 3 #define lson l, m, rt<<1

 4 #define rson m+1, r, rt<<1|1

 5 

 6 const int maxn = 200000;

 7 

 8 char cmd[2];

 9 int  n, mNum, a, b, max[maxn<<2];

10 

11 int Max(int x, int y)

12 {

13     return (x>y ? x:y);

14 }/* Max */

15 

16 void BuildTree(int l, int r, int rt)

17 {

18     if (l == r)

19     {

20         scanf("%d", &max[rt]);

21         return ;

22     }/* End of If */

23     

24     int m = (l+r)>>1;

25     BuildTree(lson);

26     BuildTree(rson);

27     max[rt] = Max(max[rt<<1], max[rt<<1|1]);    /* Push Up */

28 }/* BuildTree */

29 

30 int Query(int L, int R, int l, int r, int rt)

31 {

32     if (L<=l && r<=R)

33         return max[rt];

34     

35     int ret=-1, m=(l+r)>>1;

36 

37     if (L <= m)

38         ret = Max(ret, Query(L, R, lson));

39     if (R > m)

40         ret = Max(ret, Query(L, R, rson));

41 

42     return ret;

43 }/* Query */

44 

45 void UpData(int p, int bi, int l, int r, int rt)

46 {

47     if (l == r)

48     {

49         max[rt] = bi;

50         return ;

51     }/* End of If */

52 

53     int m = (l+r)>>1;

54 

55     if (p <= m)

56         UpData(p, bi, lson);

57     else

58         UpData(p, bi, rson);

59         

60     max[rt] = Max(max[rt<<1], max[rt<<1|1]);    /* Push Up */

61 }/* UpData */

62 

63 int main()

64 {

65     while (~scanf("%d %d", &n, &mNum))

66     {

67         BuildTree(1, n, 1);

68         for (int i=1; i<=mNum; ++i)

69         {

70             scanf("%s %d %d", cmd, &a, &b);

71             if (cmd[0] == 'Q')  /* Query */

72                 printf("%d\n", Query(a, b, 1, n, 1));

73             else    /* UpData */

74                 UpData(a, b, 1, n, 1);

75         }

76     }/* End of While */

77     

78     return 0;

79 }