【poj2761】 Feed the dogs

http://poj.org/problem?id=2761 (题目链接)

题意

　　求区间第K大。

Solution

　　同poj2104

细节

　　可能会有相同元素。

主席树代码

// poj2761
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<queue>
#define LL long long
#define lim 1000000000
#define inf 2147483640
#define Pi acos(-1.0)
#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
using namespace std;

const int maxn=100010;
int n,m,sz,rt[maxn];
struct node {
	int son[2],s;
	int& operator [] (int x) {return son[x];}
}tr[maxn*40];

void build(int &u,int v,int l,int r,int val) {
	u=++sz;
	if (l==r) {tr[u].s=tr[v].s+1;return;}
	int mid=(l+r)>>1;
	if (val<=mid) build(tr[u][0],tr[v][0],l,mid,val),tr[u][1]=tr[v][1];
	else build(tr[u][1],tr[v][1],mid+1,r,val),tr[u][0]=tr[v][0];
	tr[u].s=tr[tr[u][0]].s+tr[tr[u][1]].s;
}
int query(int u,int v,int l,int r,int k) {
	if (l==r) return l;
	int mid=(l+r)>>1,c=tr[tr[v][0]].s-tr[tr[u][0]].s;
	if (c>=k) return query(tr[u][0],tr[v][0],l,mid,k);
	else return query(tr[u][1],tr[v][1],mid+1,r,k-c);
}
int main() {
	scanf("%d%d",&n,&m);
	for (int x,i=1;i<=n;i++) {
		scanf("%d",&x);
		build(rt[i],rt[i-1],-lim,lim,x);
	}
	for (int x,y,k,i=1;i<=m;i++) {
		scanf("%d%d%d",&x,&y,&k);
		printf("%d
",query(rt[x-1],rt[y],-lim,lim,k));
	}
	return 0;
}

分块+莫队代码

// poj2761
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#define LL long long
#define inf 2147483640
#define Pi acos(-1.0)
#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
using namespace std;

const int maxn=100010;
struct ask {int l,r,k,id;}t[maxn];
struct data {int w,id;}a[maxn];
int pos[maxn],cnts[maxn],b[maxn],p[maxn],ma[maxn],ans[maxn],n,m,s,q,block;


bool wcmp(data a,data b) {
    return a.w<b.w;
}
bool poscmp(ask a,ask b) {
    return pos[a.l]==pos[b.l] ? a.r<b.r : pos[a.l]<pos[b.l];
}
void build() {
    block=(int)sqrt((float)m);
    for (int i=1;i<=m;i++) pos[i]=(i-1)/block+1;
    s=m%block ? m/block+1 : m/block;
    for (int i=1;i<=s;i++) cnts[i]=0;
}
void update(int x,int val) {
    cnts[pos[x]]+=val;
    b[x]+=val;
}
int query(int k) {
    int tot=0;
    for (int i=1;i<=s;i++) {
        tot+=cnts[i];
        if (tot>=k) {
            tot-=cnts[i];
            for (int j=(i-1)*block+1;j<=min(i*block,m);j++) {
                if (tot+b[j]>=k) return ma[j];
                else tot+=b[j];
            }
        }
    }
}
int main() {
    scanf("%d%d",&n,&q);
    for (int i=1;i<=n;i++) scanf("%d",&a[i].w),a[i].id=i;
    for (int i=1;i<=q;i++) scanf("%d%d%d",&t[i].l,&t[i].r,&t[i].k),t[i].id=i;
    sort(a+1,a+1+n,wcmp);
    m=0;
    ma[p[a[1].id]=++m]=a[1].w;
    for (int i=2;i<=n;i++) {
        if (a[i].w!=a[i-1].w) m++;
        ma[p[a[i].id]=m]=a[i].w;
    }
    block=(int)sqrt((float)n);
    for (int i=1;i<=n;i++) pos[i]=(i-1)/block+1;
    sort(t+1,t+1+q,poscmp);
    build();
    for (int l=1,r=0,i=1;i<=q;i++) {
        for (;r<t[i].r;r++) update(p[r+1],1);
        for (;r>t[i].r;r--) update(p[r],-1);
        for (;l<t[i].l;l++) update(p[l],-1);
        for (;l>t[i].l;l--) update(p[l-1],1);
        ans[t[i].id]=query(t[i].k);
    }
    for (int i=1;i<=q;i++) printf("%d
",ans[i]);
    return 0;
}