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=

#include <cstdio>
#include <cstring>

const int MAXN = 200000 + 10;

struct Node
{
    int r, l;
    int max;
    Node *l_child, *r_child;
};

Node Tree[MAXN + MAXN];
int N, M;
int cnt;

int GetMax( int a, int b )
{
    return a > b ? a : b;
}

void BuildTree( int l, int r, Node *Td )
{
    Td->l = l;
    Td->r = r;
    if ( l == r )
    {
        scanf( "%d", &Td->max );
        return;
    }

    ++cnt;
    Td->l_child = Tree + cnt;
    BuildTree( l, (l + r) / 2, Td->l_child );

    ++cnt;
    Td->r_child = Tree + cnt;
    BuildTree( (l + r) / 2 + 1, r, Td->r_child );

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

    return;
}

void Update( int ii, int &e, Node *Td )
{
    if ( ii == Td -> l && ii == Td -> r )
    {
        Td -> max = e;
        return;
    }

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

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

    return;
}

int Query( int l, int r, Node *Td )
{
    if ( l == Td -> l && r == Td -> r )
        return Td -> max;

    if ( r <= ( Td -> l + Td -> r ) / 2 ) return Query( l, r, Td -> l_child );
    else if ( l > ( Td -> l + Td -> r ) / 2 ) return Query( l, r, Td -> r_child );
    else return GetMax( Query( l, ( Td -> l + Td -> r ) / 2, Td -> l_child ),  Query( ( Td -> l + Td -> r ) / 2 + 1, r, Td -> r_child ) );
}

int main()
{
    char op[4];
    while ( scanf( "%d%d", &N, &M ) != EOF )
    {
        cnt = 0;
        BuildTree( 1, N, Tree );
        for ( int i = 0; i < M; ++i )
        {
            int a, b;
            scanf( "%s%d%d", op, &a, &b );
            switch( op[0] )
            {
                case 'Q':
                printf( "%d\n", Query( a, b, Tree ) );
                break;

                case 'U':
                Update( a, b, Tree );
                break;
            }
        }
    }
    return 0;
}