HDU 1754 I Hate It

题目链接： http://acm.hdu.edu.cn/showproblem.php?pid=1754

线段树节点更新练习

第四棵线段树……TUT……初始化的时候忘了把cnt设为0， RE了几次……=3=

 1 #include <cstdio>

 2 #include <cstring>

 3 

 4 const int MAXN = 200000 + 10;

 5 

 6 struct Node

 7 {

 8     int r, l;

 9     int max;

10     Node *l_child, *r_child;

11 };

12 

13 Node Tree[MAXN + MAXN];

14 int N, M;

15 int cnt;

16 

17 int GetMax( int a, int b )

18 {

19     return a > b ? a : b;

20 }

21 

22 void BuildTree( int l, int r, Node *Td )

23 {

24     Td->l = l;

25     Td->r = r;

26     if ( l == r )

27     {

28         scanf( "%d", &Td->max );

29         return;

30     }

31 

32     ++cnt;

33     Td->l_child = Tree + cnt;

34     BuildTree( l, (l + r) / 2, Td->l_child );

35 

36     ++cnt;

37     Td->r_child = Tree + cnt;

38     BuildTree( (l + r) / 2 + 1, r, Td->r_child );

39 

40     Td->max = GetMax( Td -> l_child -> max, Td -> r_child -> max );

41 

42     return;

43 }

44 

45 void Update( int ii, int &e, Node *Td )

46 {

47     if ( ii == Td -> l && ii == Td -> r )

48     {

49         Td -> max = e;

50         return;

51     }

52 

53     if ( ii <= ( Td -> l + Td -> r ) / 2 )

54        Update( ii, e, Td -> l_child );

55     else if ( ii > ( Td -> l + Td -> r ) / 2 ) Update( ii, e, Td -> r_child );

56 

57     Td->max = GetMax( Td -> l_child -> max, Td -> r_child -> max );

58 

59     return;

60 }

61 

62 int Query( int l, int r, Node *Td )

63 {

64     if ( l == Td -> l && r == Td -> r )

65         return Td -> max;

66 

67     if ( r <= ( Td -> l + Td -> r ) / 2 ) return Query( l, r, Td -> l_child );

68     else if ( l > ( Td -> l + Td -> r ) / 2 ) return Query( l, r, Td -> r_child );

69     else return GetMax( Query( l, ( Td -> l + Td -> r ) / 2, Td -> l_child ),  Query( ( Td -> l + Td -> r ) / 2 + 1, r, Td -> r_child ) );

70 }

71 

72 int main()

73 {

74     char op[4];

75     while ( scanf( "%d%d", &N, &M ) != EOF )

76     {

77         cnt = 0;

78         BuildTree( 1, N, Tree );

79         for ( int i = 0; i < M; ++i )

80         {

81             int a, b;

82             scanf( "%s%d%d", op, &a, &b );

83             switch( op[0] )

84             {

85                 case 'Q':

86                 printf( "%d\n", Query( a, b, Tree ) );

87                 break;

88 

89                 case 'U':

90                 Update( a, b, Tree );

91                 break;

92             }

93         }

94     }

95     return 0;

96 }