[模板]主席树

主席树其实我还是不太懂,但是就是一个数据结构,维护权值线段树,每次维护一个新的根节点,查询的时候直接把两个版本查就行了.剩下的做题去领悟吧!

poj2104

代码:

#include<iostream>
#include<cstdio>
#include<cmath>
#include<queue>
#include<algorithm>
#include<vector>
#include<cstring>
using namespace std;
#define duke(i,a,n) for(int i = a;i <= n;i++)
#define lv(i,a,n) for(int i = a;i >= n;i--)
#define clean(a) memset(a,0,sizeof(a))
#define pr pair<int,int>
#define mp make_pair
const int INF = 1 << 30;
const double eps = 1e-8;
typedef long long ll;
typedef double db;
template <class T>
void read(T &x)
{
    char c;
    bool op = 0;
    while(c = getchar(), c < '0' || c > '9')
        if(c == '-') op = 1;
    x = c - '0';
    while(c = getchar(), c >= '0' && c <= '9')
        x = x * 10 + c - '0';
    if(op) x = -x;
}
template <class T>
void write(T x)
{
    if(x < 0) putchar('-'), x = -x;
    if(x >= 10) write(x / 10);
    putchar('0' + x % 10);
}
const int MAXN = 100010;
struct node
{
    int l,r,sum;
}tree[MAXN * 20];
int cnt = 0;
void insert(int &num,int &x,int l,int r)
{
    tree[cnt++] = tree[x]; x = cnt - 1;
    ++tree[x].sum;
    if(l == r) return;
    int mid = (l + r) >> 1;
    if(num <= mid) insert(num,tree[x].l,l,mid);
    else insert(num,tree[x].r,mid + 1,r);
}
int query(int lst,int now,int k,int l,int r)
{
    if(l == r) return l;
    int mid = (l + r) >> 1;
    int t = tree[tree[now].l].sum - tree[tree[lst].l].sum;
    // int mid = (r + l) >> 1;
    if(k <= t) return query(tree[lst].l,tree[now].l,k,l,mid);
    else
    return query(tree[lst].r,tree[now].r,k - t,mid + 1,r);
}
struct A
{
    int x,idx;
    bool operator < (const A &rhs) const
    {
        return x < rhs.x;
    }
};
A a[MAXN];
int Rank[MAXN],root[MAXN];
int n,m;
int main()
{
    tree[0].l = tree[0].r = tree[0].sum = 0;
    root[0] = 0;
    while(scanf("%d%d",&n,&m) != EOF)
    {
        tree[0].l = tree[0].r = tree[0].sum = 0;
        root[0] = 0;
        duke(i,1,n)
        {
            read(a[i].x);
            a[i].idx = i;
        }
        sort(a + 1,a + n + 1);
        cnt = 1;
        duke(i,1,n)
        {
            Rank[a[i].idx] = i;
        }
        duke(i,1,n)
        {
            root[i] = root[i - 1];
            insert(Rank[i],root[i],1,n);
        }
        while(m--)
        {
            int now,lst,k;
            read(lst);read(now);read(k);
            printf("%d
",a[query(root[lst - 1],root[now],k,1,n)].x);
        }
    }
    return 0;
}