codevs 1690 线段树

“反转类问题”需要注意的是pushdown懒标记的时候要用异或（或者++%2）而不是赋值，因为它是和奇偶性有关系的。

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

const int N = 100001;

struct Node 
{
    int l, r, sum, rev;
} node[N << 2];

void pushup( int i )
{
    node[i].sum = node[i << 1].sum + node[i << 1 | 1].sum;
}

void build( int i, int l, int r )
{
    node[i].l = l, node[i].r = r, node[i].rev = node[i].sum = 0;
    if ( l == r ) return ;
    int mid = ( l + r ) >> 1;
    build( i << 1, l, mid );
    build( i << 1 | 1, mid + 1, r );
}

void pushdown( int i )
{
    if ( node[i].rev )
    {
        int lc = i << 1, rc = lc | 1;
        node[lc].rev ^= 1;
        node[rc].rev ^= 1;
        node[lc].sum = node[lc].r - node[lc].l + 1 - node[lc].sum;
        node[rc].sum = node[rc].r - node[rc].l + 1 - node[rc].sum;
        node[i].rev = 0;
    }
}

void update( int i, int l, int r )
{
    if ( node[i].l == l && node[i].r == r )
    {
        node[i].sum = node[i].r - node[i].l + 1 - node[i].sum;
        node[i].rev ^= 1;
        return ;
    }
    pushdown(i);
    int mid = ( node[i].l + node[i].r ) >> 1;
    if ( r <= mid )
    {
        update( i << 1, l, r );
    }
    else if ( l > mid )
    {
        update( i << 1 | 1, l, r );
    }
    else
    {
        update( i << 1, l, mid );
        update( i << 1 | 1, mid + 1, r );
    }
    pushup(i);    
}

int query( int i, int l, int r )
{
    if ( node[i].l == l && node[i].r == r )
    {
        return node[i].sum;
    }
    pushdown(i);
    int mid = ( node[i].l + node[i].r ) >> 1;
    if ( r <= mid )
    {
        return query( i << 1, l, r );
    }
    else if ( l > mid )
    {
        return query( i << 1 | 1, l, r );
    }
    else
    {
        return query( i << 1, l, mid ) + query( i << 1 | 1, mid + 1, r );
    }
}

int main ()
{
    int n, m;
    while ( scanf("%d%d", &n, &m) != EOF )
    {
        build( 1, 1, n );
        while ( m-- )
        {
            int op, x, y;
            scanf("%d%d%d", &op, &x, &y);
            if ( op == 0 )
            {
                update( 1, x, y );
            }
            else
            {
                printf("%d
", query( 1, x, y ));
            }
        }
    }
    return 0;
}