poj3277--City Horizon(线段树+离散化+扫描线)

Farmer John has taken his cows on a trip to the city! As the sun sets, the cows gaze at the city horizon and observe the beautiful silhouettes formed by the rectangular buildings.

The entire horizon is represented by a number line with N (1 ≤ N ≤ 40,000) buildings. Building i‘s silhouette has a base that spans locations A_i through B_i along the horizon (1 ≤ A_i < B_i ≤ 1,000,000,000) and has height H_i (1 ≤ H_i ≤ 1,000,000,000). Determine the area, in square units, of the aggregate silhouette formed by all N buildings.

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;
#define maxn 81000
#define LL __int64
struct node1
{
    LL x, y1 , y2 ;
    LL flag ;
} p[maxn<<2];
struct node2
{
    LL l , r ;
    LL sum ;
} cl[maxn<<2];
LL lazy[maxn<<2];
LL s[maxn<<2] ;
bool cmp(node1 a,node1 b)
{
    return a.x < b.x ;
}
void push_up(int rt)
{
    if( lazy[rt] )
        cl[rt].sum = cl[rt].r - cl[rt].l ;
    else
        cl[rt].sum = cl[rt<<1].sum + cl[rt<<1|1].sum ;
}
void creat(int rt,int l,int r)
{
    cl[rt].l = s[l] ;
    cl[rt].r = s[r] ;
    if( r - l > 1 )
    {
        creat(rt<<1,l,(l+r)/2);
        creat(rt<<1|1,(l+r)/2,r);
    }
    else
        cl[rt].sum = 0 ;
    return ;
}
void update(int rt,LL l,LL r,int flag)
{
    if( l == cl[rt].l && r == cl[rt].r )
    {
        lazy[rt] += flag ;
        push_up(rt);
        return ;
    }
    else
    {
        if( cl[rt<<1].r > l )
        {
            LL k = cl[rt<<1].r < r ? cl[rt<<1].r : r ;
            update(rt<<1,l,k,flag);
        }
        if( cl[rt<<1|1].l < r )
        {
            LL k = cl[rt<<1|1].l > l ? cl[rt<<1|1].l : l ;
            update(rt<<1|1,k,r,flag);
        }
        push_up(rt);
    }
}
int main()
{
    LL i , n , x1 , x2 , h , low , ans ;
    while(scanf("%I64d", &n)!=EOF)
    {
        for(i = 0 ; i < n ; i++)
        {
            scanf("%I64d %I64d %I64d", &x1, &x2, &h);
            p[i].x = x1 ;
            p[i].y1 = 0 ;
            p[i].y2 = h ;
            p[i].flag = 1 ;
            p[i+n].x = x2 ;
            p[i+n].y1 = 0 ;
            p[i+n].y2 = h ;
            p[i+n].flag = -1 ;
            s[i+1] = h ;
        }
        s[n+1] = 0 ;
        sort(s+1,s+(n+2));
        sort(p,p+2*n,cmp);
        creat(1,1,n+1);
        update(1,p[0].y1,p[0].y2,p[0].flag);
        ans = 0 ;
        for(i = 1 ; i < 2*n ; i++)
        {
            ans += ( p[i].x - p[i-1].x )*cl[1].sum;
            update(1,p[i].y1,p[i].y2,p[i].flag);
        }
        printf("%I64d\n", ans);
    }
    return 0;
}