BZOJ3295动态逆序对

一道比较傻的CDQ分治

CDQ: 主要用于解决三位偏序的问题

#include<cstdio>
#include<cctype>
#include<algorithm>
#include<cstring>
using namespace std;
inline long long read()
{
    long long x = 0, flag = 1;
    char c;
    while(! isgraph(c = getchar()))
        if(c == '-')
            flag *= - 1;
    while(isgraph(c))
        x = x * 10 + c - '0', c = getchar();
    return x * flag;
}
void println(long long x)
{
    if(x < 0)
        putchar('-'), x *= - 1;
    if(x == 0)
        putchar('0');
    long long ans[10 + (1 << 4)], top = 0;
    while(x)
        ans[top ++] = x % 10, x /= 10;
    for(; top; top --)
        putchar(ans[top - 1] + '0');
    putchar('\n');
}
const long long MAXN = (long long)1e5 + (1 << 5);
struct spot
{
    long long t, pos, w;
    spot(){}
    spot(long long t, long long pos, long long w): t(t), pos(pos), w(w){}
}a[MAXN], b[MAXN];
long long pos[MAXN];
long long operator <(spot x, spot y)
{
    if(x.t != y.t)
        return x.t < y.t;
    return x.pos < y.pos;
}
long long n;
long long ans[MAXN];
long long tree[MAXN];
void modify(long long u, long long delta)
{
    while(u <= n)
        tree[u] += delta, u += (u & (-u));
}
long long query(long long u)
{
    long long ret = 0;
    while(u)
        ret += tree[u], u -= (u & (- u));
    return ret;
}
long long cmp(spot x, spot y)
{
    return x.pos < y.pos;
}
void CDQ(long long L, long long R)
{
    if(L + 1 >= R)
        return;
    long long top = 0;
    long long mid = (L + R) >> 1;
    for(long long i = L; i < mid; i ++)
        b[top] = a[i], b[top ++].t = - 1;
    for(long long i = mid; i < R; i ++)
        b[top ++] = a[i];
    sort(b, b + top, cmp);
    long long cnt = 0;
    for(long long i = 0; i < top; i ++)
    {
        if(b[i].t == - 1)
            modify(b[i].w, 1), cnt ++;
        else
            ans[b[i].t] += query(n) - query(b[i].w);
    }
    for(long long i = 0; i < top; i ++)
        if(b[i].t == - 1)
            modify(b[i].w, - 1);
    CDQ(L, mid);
    CDQ(mid, R);
}
long long cmp2(spot x, spot y)
{
    if(x.t != y.t)
        return x.t < y.t;
    return x.pos > y.pos;
}
long long cmp1(spot x, spot y)
{
    return x.pos > y.pos;
}
void CDQ1(long long L, long long R)
{
    if(L + 1 >= R)
        return;
    long long top = 0;
    long long mid = (L + R) >> 1;
    for(long long i = L; i < mid; i ++)
        b[top] = a[i], b[top ++].t = - 1;
    for(long long i = mid; i < R; i ++)
        b[top ++] = a[i];
    sort(b, b + top, cmp1);
    long long cnt = 0;
    for(long long i = 0; i < top; i ++)
    {
        if(b[i].t == - 1)
            modify(b[i].w, 1), cnt ++;
        else
            ans[b[i].t] += query(b[i].w);
    }
    for(long long i = 0; i < top; i ++)
        if(b[i].t == - 1)
            modify(b[i].w, - 1);
    CDQ1(L, mid);
    CDQ1(mid, R);
}
int main()
{
    #ifndef ONLINE_JUDGE
    freopen("BZOJ3295.in", "r", stdin);
    freopen("BZOJ3295.out", "w", stdout);
    #endif
    n = read();
    long long m = read();
    for(long long i = 0; i < n; i ++)
        a[i].pos = i, a[i].w = read(), a[i].t = n - m, pos[a[i].w] = i;
    for(long long i = 0; i < m; i ++)
        a[pos[read()]].t = n - i;
    sort(a, a + n);
    memset(ans, 0, sizeof(ans));
    memset(tree, 0, sizeof(tree));
    CDQ(0, n);
    sort(a, a + n, cmp2);
    CDQ1(0, n);
    for(long long i = n - m + 2; i <= n; i ++)
        ans[i] += ans[i - 1];
    for(long long i = n; i > n - m; i --)
        println(ans[i]);
}

顺便, 承蒙YAY大神的指导, 学会了一个可以用来出数据的函数random_shuffle(int&, int&), 用于随机打乱区间中的元素. 附上对拍代码

#include<cstdio>
#include<cstdlib>
#include<ctime>
#include<cctype>
#include<algorithm>
using namespace std;
inline int read()
{
    int x = 0, flag = 1;
    char c;
    while(! isgraph(c = getchar()))
        if(c == '-')
            flag *= - 1;
    while(isgraph(c))
        x = x * 10 + c - '0', c = getchar();
    return x * flag;
}
void println(int x)
{
    if(x < 0)
        putchar('-'), x *= - 1;
    if(x == 0)
        putchar('0');
    int ans[10 + (1 << 4)], top = 0;
    while(x)
        ans[top ++] = x % 10, x /= 10;
    for(; top; top --)
        putchar(ans[top - 1] + '0');
    putchar('\n');
}
const int maxn=1e5+10;
int a[maxn];
int main() {
    freopen("bzoj3295.in","w",stdout);
    srand(time(0));
    int n=100000;
    printf("%d %d\n",n,n);
    for (int i=1;i<=n;++i) a[i]=i;
    random_shuffle(a+1,a+n+1);
    for (int i=1;i<=n;++i) printf("%d ",a[i]);
    puts("");
    random_shuffle(a+1,a+n+1);
    for (int i=1;i<=n;++i) printf("%d ",a[i]);
    puts("");
}

对拍用的BAT

@echo off
:loop
mkd
BZOJ3295
ni
fc BZOJ3295.out ni.out
if not errorlevel 1 goto loop
pause