poj2104--K-th Number(划分树)

Description

Input

Output

Sample Input

7 3
1 5 2 6 3 7 4
2 5 3
4 4 1
1 7 3

Sample Output

5
6
3

Hint

求第k大数,划分树的模板题

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std ;
int a[100005] , a_sort[100005] ;
int sum[20][100005] ;
int tree[20][100005] ;
void build(int c,int l,int r) {
    if( l == r ) return ;
    int mid = (l+r)/2 , m = mid-l+1 ;
    int pl = l , pr = mid + 1 , i ;
    for(i = l ; i <= mid ; i++)
        if( tree[c][i] < a_sort[mid] )
            m-- ;
    for(i = l ; i <= r ; i++) {
        if( i == l ) sum[c][i] = 0 ;
        else sum[c][i] = sum[c][i-1] ;
        if( tree[c][i] == a_sort[mid] ) {
            if( m ) {
                m-- ;
                tree[c+1][pl++] = tree[c][i] ;
                sum[c][i]++ ;
            }
            else
                tree[c+1][pr++] = tree[c][i] ;
        }
        else if( tree[c][i] < a_sort[mid] ) {
            tree[c+1][pl++] = tree[c][i] ;
            sum[c][i]++ ;
        }
        else
            tree[c+1][pr++] = tree[c][i] ;
    }
    build(c+1,l,mid) ;
    build(c+1,mid+1,r) ;
}
int query(int c,int l,int r,int ql,int qr,int k) {
    int num1 , num2 ; //num1?[l,ql) num2?[ql,qr]
    int mid = (l+r) / 2 ;
    if( l == r ) return tree[c][l] ;
    if( l == ql ) {
        num1 = 0 ;
        num2 = sum[c][qr] ;
    }
    else {
        num1 = sum[c][ql-1] ;
        num2 = sum[c][qr] - num1 ;
    }
    if( k <= num2 )
        query(c+1,l,mid,l+num1,l+num1+num2-1,k) ;
    else
        query(c+1,mid+1,r,mid+1+(ql-l-num1),mid+1+(qr-l-num1-num2),k-num2);
}
int main() {
    int n , m , l , r , k ;
    int i , j ;
    while( scanf("%d %d", &n, &m) != EOF ) {
        for(i = 1 ; i <= n ; i++) {
            scanf("%d", &a[i]) ;
            tree[0][i] = a_sort[i] = a[i] ;
        }
        sort(a_sort+1,a_sort+n+1) ;
        build(0,1,n) ;
        while( m-- ) {
            scanf("%d %d %d", &l, &r, &k) ;
            printf("%d\n", query(0,1,n,l,r,k) ) ;
        }
    }
    return 0 ;
}

poj2104--K-th Number(划分树)

原文：http://blog.csdn.net/winddreams/article/details/44858947