主席树入门——询问区间第k大pos2104，询问区间<=k的元素个数hdu4417

poj2104找了个板子。。,但是各种IO还可以进行优化

/*
找区间[l,r]第k大的数
*/
#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;
#define maxn 100005
struct Node{int lc,rc,sum;}t[maxn*];
int n,q,a[maxn],b[maxn],m,rt[maxn],size;
int build(int l,int r){
    int now=++size;
    t[now].lc=t[now].rc=t[now].sum=;
    if(l==r)return now;
    int mid=l+r>>;
    t[now].lc=build(l,mid);
    t[now].rc=build(mid+,r);
    return now;
}
int update(int last,int l,int r,int pos){//更新到pos点
    int now=++size;
     t[now]=t[last];t[now].sum++;
     if(l==r)return now;
     int mid=l+r>>;
     if(pos<=mid)t[now].lc=update(t[last].lc,l,mid,pos);
     else t[now].rc=update(t[last].rc,mid+,r,pos);
     return now;
}
int query(int st,int ed,int l,int r,int k){
    if(l==r)return l;
    int mid=l+r>>;
    int sum=t[t[ed].lc].sum-t[t[st].lc].sum;
    if(k<=sum)return query(t[st].lc,t[ed].lc,l,mid,k);
    else return query(t[st].rc,t[ed].rc,mid+,r,k-sum);
}
void debug(int x){
    cout<<t[t[rt[]].lc].sum-t[t[rt[]].lc].sum;
}
int main(){
    cin>>n>>q;
    for(int i=;i<=n;i++)cin>>a[i],b[i]=a[i];
    sort(b+,b++n);
    m=unique(b+,b++n)-(b+);
    rt[]=build(,m);
    for(int i=;i<=n;i++){
        int pos=lower_bound(b+,b++m,a[i])-b;
        rt[i]=update(rt[i-],,m,pos);
    }
    while(q--){
        int l,r,k;
        cin>>l>>r>>k;
        cout<<b[query(rt[l-],rt[r],,m,k)]<<'\n';
    }

}

hdu4417 用vector会莫名MLE，以后就用数组来进行离散化吧。另外，unique(a+1,a+1+n)函数对a数组去重，然后返回去重数组的下一位下标

#include<bits/stdc++.h>
using namespace std;
#define maxn 100005
struct Node{int lc,rc,v;}t[maxn*];
int m,tot,a[maxn],b[maxn],n,rt[maxn];

int update(int last, int l, int r, int pos){
    int now = ++ tot;
    t[now] = t[last];
    t[now].v ++;
    if(l == r) return now;
    int mid = (l + r) >> ;
    if(pos <= mid) t[now].lc = update(t[last].lc, l, mid, pos);
    else t[now].rc = update(t[last].rc, mid+, r, pos);
    return now;
}
int query(int st, int ed, int L, int R, int l, int r){
    if(L <= l && r <= R) return t[ed].v - t[st].v;
    int mid = (l + r) >> ;
    int res = ;
    if(L <= mid) res += query(t[st].lc, t[ed].lc, L, R, l, mid);
    if(R > mid) res += query(t[st].rc, t[ed].rc, L, R, mid+, r);
    return res;
}
int build(int l,int r){
    int now=++tot;
    t[now].lc=t[now].rc=t[now].v=;
    if(l==r)return now;
    int mid=l+r>>;
    t[now].lc=build(l,mid);
    t[now].rc=build(mid+,r);
    return now;
}
int main(){
    int T, Case = ;
    scanf("%d", &T);
    int n, q;
    while(T --) {
        scanf("%d %d", &n, &q);
        for(int i = ;i <= n;i ++) {
            scanf("%d", &a[i]);
            b[i] = a[i];
        }
        sort(b+, b++n);
        int m = unique(b+, b++n) - (b+);
        for(int i = ;i <= n;i ++) a[i] = lower_bound(b+, b++m, a[i]) - b;
        tot = ;
        rt[] = build(, m);
        for(int i = ;i <= n;i ++) rt[i] = update(rt[i-], , m, a[i]);
        printf("Case %d:\n", ++Case);
        while(q --) {
            int l, r, H;
            scanf("%d %d %d", &l, &r, &H);
            l ++, r ++;
            int pos = upper_bound(b+, b++m, H) - b;
            pos --;
            if(!pos) {
                puts("");
                continue;
            } else {
                printf("%d\n", query( rt[l-], rt[r], , pos, , m ) );
            }
        }
    }
    return ;
}