HDOJ 3255 Farming（扫描线 + 线段树 体积的并）

题意：

有一块田，上面有n个矩阵，每个矩阵对应一个权值，矩阵相交的部分取权值大的，问最后能获得多少值。

思路：

1. 权值问题可以转换为体积问题，因为相同格子里面权值大的胜，可以把权值看成是立方体的高，于是问题转换为立方体体积的并。

2. 和 get the treasure 题目类似，因为price变化的范围很小，于是先对高进行离散化 + 扫描。

3. 剩下的就是求 面积 * 高 了，对于面积，采取以前的常规手段，对 x 进行离散化，然后求面积的并就OK了。

#include <iostream>
#include <algorithm>
using namespace std;

#define lhs l, m, rt << 1
#define rhs m + 1, r, rt << 1 | 1

const int maxn = 61000;
int sum[maxn << 2], cnt[maxn << 2];
int price[10];
int xcord[maxn];

struct Coord {
    int x1, y1, x2, y2, p;
} cord[30010] ;

struct Segment {
    int l, r, h, v;

    Segment () { }
    Segment(int _l, int _r, int _h, int _v) 
        : l(_l), r(_r), h(_h), v(_v) { }

    bool operator < (const Segment& other)
    {
        if (h == other.h)
            return v > other.v;
        else
            return h < other.h;
    }
} seg[maxn] ;

void pushUp(int l, int r, int rt)
{
    if (cnt[rt])
        sum[rt] = xcord[r+1] - xcord[l];
    else if (l == r)
        sum[rt] = 0;
    else
        sum[rt] = sum[rt << 1] + sum[rt << 1 | 1];
}

void update(int beg, int end, int value, int l, int r, int rt)
{
    if (beg <= l && r <= end)
    {
        cnt[rt] += value;
        pushUp(l, r, rt);
        return ;
    }
    int m = (l + r) >> 1;
    if (beg <= m)
        update(beg, end, value, lhs);
    if (end > m)
        update(beg, end, value, rhs);

    pushUp(l, r, rt);
}

__int64 solve(int nn, int mm)
{
    __int64 ret = 0;

    sort(price + 1, price + mm + 1);

    for (int i = 1; i <= mm; ++i)
    {
        int n = 0, m = 0;
        for (int j = 0; j < nn; ++j)
        {
            if (cord[j].p >= price[i])
            {
                seg[n++] = Segment(cord[j].x1, cord[j].x2, cord[j].y1, 1);
                seg[n++] = Segment(cord[j].x1, cord[j].x2, cord[j].y2, -1);
                xcord[m++] = cord[j].x1;
                xcord[m++] = cord[j].x2;
            }
        }
        sort(seg, seg + n);
        sort(xcord, xcord + m);

        m = unique(xcord, xcord + m) - xcord;

        memset(sum, 0, sizeof(sum));
        memset(cnt, 0, sizeof(cnt));

        __int64 area = 0;
        for (int j = 0; j < n - 1; ++j)
        {
            int beg = lower_bound(xcord, xcord + m, seg[j].l) - xcord;
            int end = lower_bound(xcord, xcord + m, seg[j].r) - xcord - 1;
            if (beg <= end)
                update(beg, end, seg[j].v, 0, m - 1, 1);

            area += (__int64)sum[1] * (seg[j+1].h - seg[j].h);
        }
        ret += area * (price[i] - price[i-1]);
    }
    return ret;
}

int main()
{
    int cases, cc = 0;
    scanf("%d", &cases);

    while (cases--)
    {
        int n, m;
        scanf("%d %d", &n, &m);

        price[0] = 0;
        for (int i = 1; i <= m; ++i)
            scanf("%d", &price[i]);
        for (int i = 0; i < n; ++i)
        {
            scanf("%d %d %d %d %d", &cord[i].x1, &cord[i].y1, &cord[i].x2, &cord[i].y2, &cord[i].p);
            cord[i].p = price[cord[i].p];
        }

        printf("Case %d: %I64d\n", ++cc, solve(n, m));
    }
    return 0;
}