bzoj 1227 SDOI2009 虔诚的墓主人

    思路还是蛮清晰的

　　ask:

　　    x = t[nowright-1] - t[nowleft]

　　get_ans:
　　     ans += C(l[nowleft],k) * C(r[nowright],k) * x

　　update:
　　    t[i] = t[i] - C(up[i],k) * C(down[i],k) + C(up[i]-1,k) * C(down[i]+1,k)

　　sort:
　　y first
　　x second

    组合数的递推公式都忘了……

    C (i, j) = C (i-1, j) + C (i-1, j-1)

    这道题模比较大，乘的时候要注意不爆 long long

    上代码：

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <iostream>
#include <cmath>
#include <map>
#define yu 2147483648LL
#define N 100100
using namespace std;

struct sss
{
    int x, y;
}dian[N];
int n, K, linenum = 0;
long long ans = 0, t[N] = {0};
map <int, int> qx, qy, rank;
int up[N], down[N], fan[N];
long long C[N][11] = {0};

bool cmp(sss a, sss b) { return a.y == b.y ? a.x < b.x : a.y < b.y; }

int lowbit(int x) { return x & -x; }

void add(int now, int addnum)
{
    addnum %= yu;
    while (now <= linenum)
    {
        t[now] += addnum;
        while (t[now] > yu) t[now] -= yu;
        now += lowbit(now);
    }
}

long long ask(int now)
{
    long long zan = 0;
    while (now)
    {
        zan += t[now];
        while (zan > yu) zan -= yu;
        now -= lowbit(now);
    }
    return zan%yu;
}

void makeC()
{
    C[0][0] = 1;
    for (int i = 1; i <= n; ++i)
    {
        C[i][0] = 1;
        for (int j = 1; j <= min(i, K); ++j)
        {
            C[i][j] = C[i-1][j-1] + C[i-1][j];
            while (C[i][j] > yu) C[i][j] -= yu;
        }
    }
}

void beforework()
{
    int xz[N]; makeC();
    for (int i = 1; i <= n; ++i) xz[i] = dian[i].x;
    sort(xz+1, xz+1+n); xz[0] = -1;
    for (int i = 1; i <= n; ++i)
        if (xz[i] != xz[i-1])
        {
            rank[xz[i]] = ++linenum;
            fan[linenum] = xz[i];
        }
    for (int i = 1; i <= linenum; ++i)
    { up[i] = qx[fan[i]]; down[i] = 0; }
}

void get_ans()
{
    int ybefore = -1, l, r;
    long long x;
    int i = 1;
    while (i <= n)
    {
        if (dian[i].y != ybefore)
        {
            l = 1; r = qy[dian[i].y]-1;
            ybefore = dian[i].y;
            int d = rank[dian[i].x];
            add(d, C[up[d]-1][K] * C[down[d]+1][K] - C[up[d]][K] * C[down[d]][K]);
            up[d]--; down[d]++;
        }
        else
        {
            x = ask(rank[dian[i].x]-1) - ask(rank[dian[i-1].x]);
            if (x < 0) x += yu;
            ans += (((x * C[l][K])%yu) * C[r][K])%yu;
            l += 1; r -= 1;
            while (ans > yu) ans -= yu;
            int d = rank[dian[i].x];
            add(d, C[up[d]-1][K] * C[down[d]+1][K] - C[up[d]][K] * C[down[d]][K]);
            up[d]--; down[d]++;
        }
        i++;
    }
}

int main()
{
    scanf("%d%d%d", &n, &n, &n);
    for (int i = 1; i <= n; ++i)
    {
        scanf("%d%d", &dian[i].x, &dian[i].y);
        qx[dian[i].x] ++; qy[dian[i].y] ++;
    }
    scanf("%d", &K);
    sort(dian+1, dian+1+n, cmp);
    beforework();
    get_ans();
    printf("%I64d\n", ans%yu);
}