HDU 1540 Tunnel Warfare

线段树点修改+区间合并

对于如何查询连续某块的端点和长度还不太熟……但是属于经典常见操作。

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>

using namespace std;

#define lc rt << 1
#define rc rt << 1 | 1
#define lson l, m, rt << 1
#define rson m + 1, r, rt << 1 | 1

const int MAXN = 50002;

int N, Q;
int stack[MAXN];
int top;
int len[ MAXN << 2 ];
int Llen[ MAXN << 2 ];
int Rlen[ MAXN << 2 ];
bool lbd[ MAXN << 2 ];
bool rbd[ MAXN << 2 ];

void PushUp( int rt, int l, int r, int m )
{
    len[rt] = max( len[lc], len[rc] );
    if ( rbd[lc] && lbd[rc] )
        len[rt] = max( len[rt], Llen[rc] + Rlen[lc] );

    lbd[rt] = lbd[lc];
    rbd[rt] = rbd[rc];

    Llen[rt] = Llen[lc];
    Rlen[rt] = Rlen[rc];

    if ( Llen[lc] == m - l + 1 ) Llen[rt] += Llen[rc];
    if ( Rlen[rc] == r - m ) Rlen[rt] += Rlen[lc];

    return;
}

void build( int l, int r, int rt )
{
    if ( l == r )
    {
        lbd[rt] = rbd[rt] = true;
        len[rt] = 1;
        Llen[rt] = Rlen[rt] = 1;
        return;
    }

    int m = ( l + r ) >> 1;
    build( lson );
    build( rson );
    PushUp( rt, l, r, m );
    return;
}

void Update( int L, int c, int l, int r, int rt )
{
    if ( L == l && L == r )
    {
        len[rt] = Llen[rt] = Rlen[rt] = c;
        if ( c == 1 ) lbd[rt] = rbd[rt] = true;
        else lbd[rt] = rbd[rt] = false;
        return;
    }

    int m = ( l + r ) >> 1;
    if ( L <= m ) Update( L, c, lson );
    else Update( L, c, rson );
    PushUp( rt, l, r, m );

    return;
}

int Query( int L, int l, int r, int rt )
{
    if ( l == r || !len[rt] || len[rt] == r - l + 1 ) return len[rt];
    int m = ( l + r ) >> 1;
    if ( L <= m )
    {
        if ( L > m - Rlen[lc] ) return Query( L, lson ) + Query( m + 1, rson );
        else return Query( L, lson );
    }
    else
    {
        if ( L < m + 1 + Llen[rc] ) return Query( m, lson ) + Query( L, rson );
        else return Query( L, rson );
    }
}

int main()
{
    //freopen( "in.txt", "r", stdin );
    //freopen( "out.txt", "w", stdout );
    while ( ~scanf( "%d%d", &N, &Q ) )
    {
        build( 1, N, 1 );
        top = 0;
        while ( Q-- )
        {
            char str[4];
            scanf( "%s", str );
            if ( str[0] == 'R' )
            {
                if ( top > 0 )
                    Update( stack[top--], 1, 1, N, 1 );
            }
            else
            {
                int a;
                scanf( "%d", &a );
                if ( str[0] == 'D' )
                {
                    Update( a, 0, 1, N, 1 );
                    stack[ ++top ] = a;
                }
                else
                    printf( "%d\n", Query( a, 1, N, 1 ) );
            }
        }
    }
    return 0;
}